Threat Explorer

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17 July 2001
13 February 2007
Also Known As:
VBS.Yang@mm, I-Worm.Yang

This worm contains a bug that prohibits it from replicating.

The bug is trivial to fix and for that reason the writeup is aimed at providing information to you about the functionality of this worm when the bug is fixed (Note: NAV will also detect the fixed worm sample).

For this worm to replicate, the operating system must be Windows XP or the Microsoft Outlook 2000 View Control must be installed.

It sends itself out to all recipients in your Microsoft Outlook address book, and overwrite all files that have ht in their extension (such as .htm and .html).

NOTE: Definitions dated prior to July 19, 2001 will detect this worm as VBS.Yang@mm

Antivirus Protection Dates

  • Initial Rapid Release version 17 July 2001
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 17 July 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 activated this worm:
  • Sends itself to all recipients in your Microsoft Outlook address book (if the following registry value does not exist).
  • Creates the value

    VBS.YangMsg VBS.YangMsg@mm

    in the registry key


  • Infects files on all attached drives.
Displays the following message:

The message that is sent by the worm has a HTML message body. It is as follows:

Subject:   Fw: Free Porno XXX Sites!!
Message: There's some great links at <site name removed>. P.S. Don't tell your BOSS! :-)

The message also contains its replication code in a <SCRIPT>...</SCRIPT> section.

This worm overwrites (with itself) all files on all on attached hard disks (this includes mapped network drives) that have the string ht in their file extension, such as .htm and .html.

All files that are overwritten are destroyed.


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.

Run LiveUpdate to make sure that you have the most recent virus definitions.
  1. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is set to scan all files.
  2. Delete any files detected as VBS.XPJunexp.intd
  3. Files that were overwritten by the worm must be restored from a clean backup.

Writeup By: Atli Gudmundsson