WORM_BRONTOK.WBK
Worm:Win32/Brontok.FFV (Microsoft), HEUR:Trojan.Win32.Generic (Kaspersky), W32.SillyFDC (Symantec), I-Worm/Brontok.AC (AVG), W32/Brontok-CJ (Sophos), W32/IRCBot.PBR!tr (Fortinet), Win32/VB.NJG worm (Nod32), W32/Brontok.EX.worm (Panda), Backdoor.Win32.IRCBot.pbr (v) (Sunbelt)
Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

Threat Type: Worm
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
This worm arrives via removable drives. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
It creates certain registry entries to prevent execution of files with certain file types.
It drops copies of itself in all removable drives.
TECHNICAL DETAILS
Arrival Details
This worm arrives via removable drives.
It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
Installation
This worm drops the following files:
- %System Drive%\(Read Me)Pendekar Blank.txt
It drops the following component file(s):
- %System Drive%\msvbvm60.dll
- %System%\dllchache\msvbvm60.dll
- %System%\dllcache\msvbvm60.dll
(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)
It drops the following copies of itself into the affected system:
- %System Drive%\AUT0EXEC.BAT
- %System%\M5VBVM60.EXE
- %System%\rund1132.exe
- %System%\dllchache.exe
- %System%\dllcache\Regedit32.com
- %System%\dllcache\Shell32.com
- %System%\dllchache\Unoccupied.reg
- %System%\dllchache\Zero.txt
- %System%\dllchache\Blank.doc
- %System%\dllchache\Empty.jpg
- %System%\dllchache\Hole.zip
- %Windows%\system32.exe
It creates the following folders:
- %System%\dllchache
(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)
Autostart Technique
This worm adds the following registry entries to enable its automatic execution at every system startup:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Secure64 = "%System%\dllcache\Regedit32.com StartUp"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Secure32 = "%System%\dllcache\Shell32.com StartUp"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Blank AntiViri = "%System Root%\AUT0EXEC.BAT StartUp"
It modifies the following registry entries to ensure it automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe, "%System%\M5VBVM60.EXE StartUp""
(Note: The default value data of the said registry entry is "%System%\userinit.exe,".)
It modifies the following entry(ies) to allow itself to run on safe mode:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\SafeBoot
AlternateShell = "%System Root%\AUT0EXEC.BAT StartUp"
(Note: The default value data of the said registry entry is "cmd.exe".)
Other System Modifications
This worm modifies the following registry entries:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideFileExt = 1
(Note: The default value data of the said registry entry is "0".)
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = 0
(Note: The default value data of the said registry entry is "1".)
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
CabinetState
FullPath = 1
(Note: The default value data of the said registry entry is "0".)
It creates the following registry entries to prevent execution of files with certain file types:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
comfile\shell\open\
command
(default) = "%System%\rund1132.exe %1"
(Note: The default value data of the said registry entry is ""%1" %*".)
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
txtfile\shell\open\
command
(default) = "%System%\rund1132.exe %1"
(Note: The default value data of the said registry entry is "%System%\NOTEPAD.EXE %1".)
Propagation
This worm drops copies of itself in all removable drives.
Dropping Routine
This worm sets the attributes of its dropped file(s) to the following:
- Read Only
- Hidden
- System
SOLUTION
Step 1
Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.
Step 2
Identify and delete files detected as WORM_BRONTOK.WBK using either the Startup Disk or Recovery Console
Step 3
Delete this registry value
Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- Secure64 = "%System%\dllcache\Regedit32.com StartUp"
- Secure64 = "%System%\dllcache\Regedit32.com StartUp"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- Secure32 = "%System%\dllcache\Shell32.com StartUp"
- Secure32 = "%System%\dllcache\Shell32.com StartUp"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
- Blank AntiViri = "%System Root%\AUT0EXEC.BAT StartUp"
- Blank AntiViri = "%System Root%\AUT0EXEC.BAT StartUp"
Step 4
Restore this modified registry value
Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.
- In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot
- From: AlternateShell = "%System Root%\AUT0EXEC.BAT StartUp"
To: AlternateShell = "cmd.exe"
- From: AlternateShell = "%System Root%\AUT0EXEC.BAT StartUp"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
- From: Userinit = "%System%\userinit.exe, "%System%%\M5VBVM60.EXE StartUp""
To: Userinit = "%System%\userinit.exe,"
- From: Userinit = "%System%\userinit.exe, "%System%%\M5VBVM60.EXE StartUp""
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: HideFileExt = "1"
To: HideFileExt = "0"
- From: HideFileExt = "1"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: ShowSuperHidden = "0"
To: ShowSuperHidden = "1"
- From: ShowSuperHidden = "0"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\CabinetState
- From: FullPath = "1"
To: FullPath = "0"
- From: FullPath = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Classes\comfile\shell\open\command
- From: (default) = "%System%\rund1132.exe %1"
To: (default) = ""%1" %*"
- From: (default) = "%System%\rund1132.exe %1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Classes\txtfile\shell\open\command
- From: (default) = "%System%\rund1132.exe %1"
To: (default) = "%System%\NOTEPAD.EXE %1"
- From: (default) = "%System%\rund1132.exe %1"
Step 5
Search and delete these folders
- %System%\dllchache
Step 6
Search and delete this file
- %System Drive%\AUT0EXEC.BAT
- %System%\M5VBVM60.EXE
- %System%\rund1132.exe
- %System%\dllchache.exe
- %System%\dllcache\Regedit32.com
- %Windows%\system32.exe
- %System Drive%\msvbvm60.dll
- %System%\dllchache\msvbvm60.dll
- %System%\dllcache\msvbvm60.dll
- %System Drive%\(Read Me)Pendekar Blank.txt
Step 7
Scan your computer with your Trend Micro product to delete files detected as WORM_BRONTOK.WBK. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.
Did this description help? Tell us how we did.