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08 June 2001
13 February 2007
Also Known As:
VBS.Fiber, VBS.Ruzz

VBS.Phybre is Visual Basic Script (VBS) Trojan horse. It copies itself into the \Windows\System folder as VBS.Phybre.vbs and modifies the registry so that this file is executed when Windows starts. If the current minute is :39, then the script's payload is activated as follows:
  • A message is displayed that indicates how many times the script has been run and how many times you have been notified of its presence.
  • It attempts to configure the registry so that the script is executed any time that an .htm or .html file is opened on the computer.

When VBS.Phybre is executed, it does the following:
  1. It copies itself to the \Windows\System folder as the file VBS.Phybre.vbs.
  2. It then creates the value


    in the registry key


    and sets it equal to the location of the VBS.Phybre.vbs file. This ensures that the script is executed when Windows starts.
  3. Next, it creates the following registry keys:



    These keys are use to maintain counts of the number of times the Trojan has run and how many times the notification message has been displayed. If the payload is triggered (when the current minute is :39), the value of the data associated with these keys is displayed in a message.
  4. The registry key


    is also modified. The value (Default) is created and set equal to C:\Windows\System\Phybre.vbs. This is an attempt to force the execution of the script any time that an .htm or .html file is opened. However, due to an incorrect file name, this action does not occur. The (Default) value that is already present in this key is not deleted, and the original (Default) value should point to the default Web browser.


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 Trojan, delete files detected as VBS.Phybre, and remove the changes that it made to the registry.

To remove the Trojan:
  1. Run LiveUpdate to make sure that you have the most recent virus definitions.
  2. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is set to scan all files.
  3. Delete files detected as VBS.Phybre.

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 click OK. The Registry Editor opens.
  3. Navigate to and delete the following keys:


  4. Navigate to the following key:

  5. In the right pane, delete the value

    (Default)   C:\Windows\System\Phybre.vbs

    CAUTION: Make sure that you delete the key that points to C:\Windows\System\Phybre.vbs. Do not delete the (Default) key that points to your Web browser.

  6. Exit the Registry Editor

Writeup By: Brian Ewell