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.Freelink

VBS.Freelink

Discovered:
02 July 1999
Updated:
13 February 2007

VBS.Freelink is an encrypted worm that works under Windows 98, Windows 2000, and all the other Windows versions that support the VBScripting language. Once the worm is launched, it uses Microsoft Outlook to automatically send an email with an attachment of itself.

Antivirus Protection Dates

  • Initial Rapid Release version 08 July 1999
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 08 July 1999
  • 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.

Similar to the Melissa virus, this worm uses MAPI calls to obtain user profiles from Microsoft Outlook. The email generated by this worm is:

Subject:

Check this
Have fun with these links. Bye.

When the attached file is executed, it creates the files:

C:\Windows\Links.vbs
C:\Windows\System\Rundll.vbs
    It also creates the file Links.vbs in the root of all mapped network drives. Next, the worm adds the value:


    Rundll   RUNDLL.VBS

    to the registry key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

    sot that ir runs each time that Windows starts.

    After infecting a system, it displays a the dialog box:

    Free XXX links
    This will add a shortcut to
    free XXX links on your desktop.
    Do you want to continue.

    If you click Yes, it creates a shortcut pointing to an adult Web site.

    It also searches for Mirc32.exe and Pirch98.exe in C:\Mirc , C:\Pirch98, C:\Program Files, and in their subfolders. If it finds either of these programs, it modifies the corresponding Script.ini or Events.ini file, so that Links.vbs is sent to other people during the IRC sessions.


    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 worm, you need to remove an entry that it made in the registry, and then run a full system scan, and delete files detected as VBS.FreeLink

    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 then click Run. The Run dialog box appears.
    2. Type regedit and then click OK. The Registry Editor opens.
    3. Navigate to the following subkey:

      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    4. In the right pane, delete the following value:

      Rundll     Rundll32.vbs
    5. Click Registry and then click Exit to save the changes.

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


    Writeup By: Abid Oonwala