WORM_VB.FAT
Worm:Win32/Backterra.F (Microsoft), W32/Bactera.worm!p2p (McAfee), Win32/VB.NIS worm (Eset), W32.Bactera (Symantec)
Windows 2000, Windows XP, Windows Server 2003
Threat Type: Worm
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
This worm arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.
TECHNICAL DETAILS
Arrival Details
This worm 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 then creates the following non-malicious file(s):
- %System%\scvhost.ini
(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)
It drops the following copies of itself into the affected system:
- %System%\scvhost\svchost.exe
- %System%\scvhost\wuauserv.exe
(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)
It creates the following folders:
- %System%\scvhost
(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)
Autostart Technique
This worm modifies the following registry entry(ies) to enable its automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "Userinit.exe, %System%\scvhost\svchost.exe, wuauserv.exe"
(Note: The default value data of the said registry entry is "Userinit.exe".)
Other System Modifications
This worm modifies the following registry key(s)/entry(ies) as part of its installation routine:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SHOWALL
CheckedValue = "0"
(Note: The default value data of the said registry entry is "1".)
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "2"
(Note: The default value data of the said registry entry is "1".)
Propagation
This worm drops the following copy(ies) of itself in all removable drives:
- {removable drive}:\desktop.exe
It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.
The said .INF file contains the following strings:
[AutoRun]
shell=verb1
shell\verb1\command=desktop.exe
shell=Auto
SOLUTION
Step 1
For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.
Step 2
Restart in Safe Mode
Step 3
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\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
- From: Userinit = "Userinit.exe, %System%\scvhost\svchost.exe, wuauserv.exe"
To: Userinit = "Userinit.exe"
- From: Userinit = "Userinit.exe, %System%\scvhost\svchost.exe, wuauserv.exe"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SHOWALL
- From: CheckedValue = "0"
To: CheckedValue = "1"
- From: CheckedValue = "0"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: Hidden = "2"
To: Hidden = "1"
- From: Hidden = "2"
Step 4
Search and delete these folders
- %System%\scvhost
Step 5
Search and delete this file
- {removable drive}:\autorun.inf
- %System%\scvhost.ini
Step 6
Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_VB.FAT. 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.