Threat Explorer

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24 April 2003
13 February 2007
Systems Affected:
Microsoft IIS, Windows

VBS.Lavra.Worm.gen is a generic detection for a class of worms that spread over file-sharing networks. It may delete files that antivirus and firewall software use.

When VBS.Lavra.Worm.gen is executed, sometimes it displays a message box that has "LVG" in the title bar.

When VBS.Lavra.Worm.gen is executed, it may do some or all of the following:
  1. Copy itself to C:\Windows or C:\Winnt. The filenames vary, but typically have the form "Larva<anything>.vbs."
    For example:
    • LarvaScript.vbs
    • LarvaV1.vs4.vbs

  2. Delete the files from the following folders, if they exist:
    • C:\AntiViral Toolkit Pro
    • C:\Program Files\Command Software\F-PROT95
    • C:\Program Files\McAfee\VirusScan
    • C:\Program Files\Norton AntiVirus
    • C:\Toolkit\FindVirus
    • C:\Program Files\Panda Software\Panda Antivirus Titanium
    • C:\Program Files\Zone Labs\ZoneAlarm
    • C:\Program Files\Tiny Personal Firewall

      NOTE: Other folders that antivirus or firewall programs use may also be affected.

  3. Modify the registry keys that antivirus programs use. For example, by setting the value:


    in the registry key:


  4. Creates six copies of itself in the folders that file-sharing programs use. The filenames vary, but all have a .vbs extension. VBS.Lavra.Worm.gen uses the following folders, if they exist:
    • Grokster:
      • C:\Program Files\Grokster\My Grokster
      • C:\archiv~1\Grokster\My Grokster
    • Morpheus:
        • C:\Program Files\Morpheus\My Shared Folder
        • C:\archiv~1\Morpheus\My Shared Folder
    • ICQ:
        • C:\Program Files\ICQ\shared files
        • C:\archiv~1\ICQ\shared files
    • Bearshare:
        • C:\Program Files\Bearshare\Shared
        • C:\archiv~1\Bearshare\Shared
    • KaZaA:
        • C:\Program Files\KaZaA\My Shared Folder
        • C:\archiv~1\KaZaA\My Shared Folder

  5. Sets itself to run at the startup of Windows 95/98/Me systems, by adding the following lines to the C:\Autoexec.bat file:

    @Start C:\Windows\<file name.vbs>
    @Start C:\Winnt\<file name.vbs>

    where <file name.vbs> is the same as the filename mentioned in step 1.

  6. Adds the string values:

    "LARVA"="C:\windows\<file name.vbs>"
    "LARVAx"="C:\winnt\<file name.vbs>"

    to the registry key:


    where <file name.vbs> is the same as the filename mentioned in step 1.

  7. Displays a message box with various messages. By default, the title bar dispalys the text, "LVG."


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.

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
  1. Update the virus definitions.
  2. Run a full system scan and delete all the files detected as VBS.Lavra.Worm.gen, or similar name detections beginning with VBS.Lavra.
  3. Delete any values that were added to the registry.
  4. Restore the deleted programs, if required.
For specific details on each of these steps, read the following instructions.

NOTE: If Norton AntiVirus does not run, the worm may have deleted the files that it needs. In this case, first follow the instructions in section 3, re-install Norton AntiVirus, and then follow the instructions in sections 1 and 2.
1. 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 here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

2. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program 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.Lavra.Worm.gen, or variants like VBS.Lavra.X.Worm (where X can be any letter), click Delete.

3. Deleting the value from the registry

CAUTION : Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit

    Then click OK. (The Registry Editor opens.)
  3. Navigate to the key:

  4. In the right pane, delete any values similar to:

    "LARVA"="C:\windows\<file name.vbs>"
    "LARVAx"="C:\winnt\<file name.vbs>"
  5. Exit the Registry Editor.

4. Restoring the deleted files
If the virus deleted the files (typically antivirus or firewall software), you will need to replace them, by either restoring them from a backup copy or by re-installing the software.
Writeup By: Heather Shannon