Threat Explorer

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16 August 2001
13 February 2007
Also Known As:

This worm sends email to all contacts in your Microsoft Outlook address book. The message contains a link to the virus writers home page. The worm also modifies mIRC settings.

Antivirus Protection Dates

  • Initial Rapid Release version 17 August 2001
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 17 August 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 it is executed, the worm copies itself as the hidden file:


It adds the value

MircProtection   c:\Io.vbs

to the registry key


This will cause the worm to run each time that Windows starts.

If the io.vbs already exists, the worm then creates the file System in the \Windows\System or \Winnt\System32 folder. (The file name is just System, with no file extension.) It then adds mIRC.ini commands to this file.

Next, it searches all drives for Mirc.ini files. If found, it appends an "include" command that points to the dropped System file.

Next, it sends an email message to all contacts in your Microsoft Outlook address book. The email is sent as a Blind Carbon Copy (BBC), and is as follows:

Subject: 'FWD: Protect your computer for free!!'

Still surfing the web unprotected? Hackers could be watching your every move. Your files could be infected, unless you're protected. Get it fast and FREE. Simple to use and downloads in seconds. -=-=-=-=-=-=-=-=-=- <Address of the virus writers Web site has been removed>.

Finally it adds a the registry key HKEY_LOCAL_MACHINE\MircProctection and sets the value to 1 to indicate it has sent the emails so that they are only sent one time.


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, delete all files detected as VBS.Thea.A, remove the value that it added to the registry \Run key, and verify that your mIRC settings are correct.

To remove the worm:
  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. Be sure that NAV is configured to scan all files.
  3. Delete all files that are detected as VBS.Thea.A.

To edit the registry:

CAUTION : We strongly recommend that you back up the system registry before you make any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure that you modify only the keys specified. Please see the document How to back up the Windows registry before you proceed.
  1. Click Start, and click Run. The Run dialog box appears.
  2. Type regedit and then click OK. The Registry Editor opens.
  3. Navigate to the following key:

  4. In the right pane, delete the following value:

    MircProtection   c:\Io.vbs
  5. Exit the registry editor.

    NOTE: It is not necessary to remove the MircProtection key that the worm added.

To check mIRC settings:
If you are using mIRC, the worm may have changed some of the settings in the Micr.ini file. Please see your mIRC documentation for the correct settings.
Writeup By: David Adamczyk