1. Symantec/
  2. Security Response/
  3. VBS.Bryon@mm


Risk Level 1: Very Low

November 13, 2003
February 13, 2007 12:13:32 PM
Systems Affected:

VBS.Bryon@mm is a mass-mailing worm. This worm uses a simple encoding. When the worm is executed, it begins by decoding itself. After decoding, this worm performs the following actions:
  1. Creates the files:
    • C:\Message.vbs
    • %Windir%\Tasksys.vbs
    • %Windir%\Message.vbs
    • %System%\Message.vbs
    • %System%\Helpdesk.vbs
    • %System%\Asl.vbs
    • %System%\Welcome.vbs
    • %System%\Fwtwih.vbs
    • %Temp%\Message.vbs
    • %System%\Flps.vbs

      %Windir% is a variable. The worm locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies the files to that location.
      -- %System% is a variable. The worm locates the System folder and copies the files to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
      --%Temp% is a variable. The worm locates the temporary folder and copies the file to that location. By default, this is C:\Windows\TEMP (Windows 95/98/Me), or C:\WINNT\Temp (Windows NT/2000), or C:\Document and Settings\<UserName>\Local Settings\Temp (Windows XP).
      -- Some of these files will be detected as VBS.LoveLetter.Var.

  2. Creates the values:


    in the registry keys:



    so that the worm runs when you start Windows.

  3. Attempts to email the first 100 entries in the Windows Address Book (.wab file). The email message will have the following characteristics:

    Subject: Mail delivery failed: returning message to sender.

    This message was create automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients [see above from address]. This is a permanent error. A copy of the message, include all the headers, is attached.

    Attachment: Message.vbs

  4. Attempts to spread over the Local Area Network by copying itself to all the folders on all the mapped drives as Message.vbs.

  5. Modifies the mIRC Script.ini file so that it automatically sends a copy of the worm to each user that joins the same channel as an infected computer.

  6. Attempts to copy itself to the A drive (floppy drive) every 20 minutes, if the drive is accessible.


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.
Writeup By: Paul Mangan
Summary| Technical Details| Removal

Search Threats

Search by name
Example: W32.Beagle.AG@mm
STAR Antimalware Protection Technologies
2016 Internet Security Threat Report, Volume 21
  • Twitter
  • Facebook
  • LinkedIn
  • Google+
  • YouTube