Threat Explorer

The Threat Explorer is a comprehensive resource consumers can turn to for daily, accurate, up-to-date information on the latest threats, risks and vulnerabilities.

VBS.Clex

VBS.Clex

Discovered:
04 February 2004
Updated:
13 February 2007
Also Known As:
Trojan.VBS.Clex [Kaspersky]
Systems Affected:
Windows

VBS.Clex is a Visual Basic script that modifies the C:\Autoexec.bat file.

When VBS.Clex is executed, it displays the message:

Title: "To unify the TanWai by China!"

Message: "The People's Republic of China Banzai!"

If you click the Yes button and close the message box, it overwrites the C:\Autoexec.bat file with the following content:

CLS
@ECHO Warning! illegal access error!
@ECHO a fatal BIOS error,be incapable of data to load......
@ECHO OFF
:USA
GOTO :USA


Then, it attempts to shut down the system.



The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Run a full system scan and repair all the files detected as VBS.Clex.
  4. Windows 95/98/Me only: Fix the C:\Autoexec.bat file.

For specific details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Scanning for and repairing the infected files
  1. Start your Symantec antivirus software and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with VBS.Clex, click Repair.

4. Fixing the C:\Autoexec.bat file
If you are using Windows 5/98/Me, do one of the following:
  • Replace the Autoexec.bat file with a clean backup copy that was made before the infection.
  • Follow these steps to delete the overwritten contents:
    1. Click Start, and then click Run.
    2. Type the following, and then click OK.

      edit c:\autoexec.bat


      (The MS-DOS Editor opens.)

    3. Delete all the lines in the file.
    4. Exit the MS-DOS Editor, and then click Yes when you are prompted to save changes.



Writeup By: Keiichi Ito