Threat Explorer

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VBS.Beast.C

VBS.Beast.C

Discovered:
07 March 2001
Updated:
13 February 2007

This is a encrypted Visual Basic script. If executed, it appends its code to all .vbs files found on the current drive. It creates the file W95inf32.vbs in the \Windows\System folder. The registry is modified to execute this file when the computer starts. This script does not contain a means by which it can transmit itself.

Antivirus Protection Dates

  • Initial Rapid Release version 07 March 2001
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 07 March 2001
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date pending
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When executed, VBS.Beast.B does the following:
  1. It appends itself to all .vbs files found on the current drive.
  2. It creates the \Windows\System\W95inf32.vbs file.
  3. It adds the value

    Beast   <path>\W95inf32.vbs

    to the registry key

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

    This executes the script when Windows starts.
  4. If the date is the 13th of the month, the script displays the following message:


Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

To remove this virus, delete the \Windows\System\W95inf32.vbs file and remove the value "Beast" from the \Run key in the registry. Restore overwritten files if needed. Here are the instructions:

To delete the W95inf32.vbs file:
  1. Using Windows Explorer, browse to the \Windows\System folder and locate the W95inf32.vbs file.
  2. Select the file, press Delete, and then click Yes to confirm.

To edit the registry:

CAUTION : We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure you modify only the keys specified. Please see the document How to back up the Windows registry before proceeding.
  1. Click Start, and click Run. The Run dialog box appears.
  2. Type regedit and then click OK. The Registry Editor opens.
  3. Navigate to the following key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
  4. In the right pane, select the value

    Beast  <path>\W95inf32.vbs
  5. Press Delete, and then click Yes to confirm.
  6. Close the Registry Editor.

To restore overwritten files (optional):
If .vbs files were overwritten, you can restore them by opening them in a text editor and deleting all of the viral code from the end of the script file.


Writeup By: Brian Ewell