Threat Explorer

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23 October 2003
13 February 2007
Also Known As:
Systems Affected:

VBS.Confi is a Visual Basic Script (VBScript) virus that spreads through floppy disks. When it is executed, it launches a "windowbomb" by repeatedly opening Web browser windows. The 11th time that this virus is executed, it replaces the "Winstart.bat" file with commands to delete all the files on the A, C, D, and E drives.

This virus consists of a VBScript embedded in a .htt (hypertext template) file. Windows normally uses the .htt files to control how folders are displayed in Windows Explorer. VBS.Confi uses this mechanism to ensure that the virus is executed every time a folder is opened. It is possible to infect a computer with VBS.Confi, by viewing the contents of an infected floppy disk with Windows Explorer.

The presence of the file MSkernel32.con or MSkernel.con is a sign of possible infection.

Virus definitions dated prior to October 24, 2003 may detect this threat as JS.Exception.Exploit.

Antivirus Protection Dates

  • Initial Rapid Release version 24 October 2003
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 24 October 2003
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date 29 October 2003
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When VBS.Confi is executed, it:
  1. Modifies various registry settings to disrupt the normal system operation:

    • Sets the value:


      in the registry key:


    • Sets the values:


      in the registry key:


    • Sets the value:


      in the registry key:


    • Sets the values:


      in the registry key:


  2. Copies itself as:
    • %Windir%\System\MSkernel32.con
    • %Windir%\System\MSkernel.con

      if it is run from a floppy disk, or as:

    • A:\folder.htt
    • A:\desktop.ini

      if it is run from the %Windir%\System directory.

      Note: %Windir% is a variable. The virus locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies itself to the System subdirectory.

  3. Sets the ".con" extension to be synonymous with the ".htt" (hypertext template) extension by creating the following registry keys:


  4. Sets itself to be the default template used to view folders with Windows Explorer, by setting the value:

    "PersistMoniker"="file:/ /%Windir%\system\MSkernel32.con"

    in the registry key:


  5. Repeatedly pops up Internet Explorer windows. This will likely cause the system to become unresponsive, requiring a restart.

  6. Increments a counter, stored in the registry as:

    HKEY_LOCAL_MACHINE\Software\Microsoft\MediaPlayer\Setup\Meta Status.

    The 11th time the virus is executed, it creates or overwrites %Windir%\Winstart.bat with commands to run deltree on the A:, C:, D:, and E: drives. On Windows 95/98 systems, the commands will be executed the next time Windows is rebooted.

    The malicious Winstart.bat file is detected as BAT.Trojan.


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.

What you need to do depends on whether the Trojan has actually executed.

If VBS.Confi has already executed
If VBS.Confi has run 10 or fewer times, it has made numerous system modifications that make manual repair difficult. The easiest method to fix it is to restore the entire registry from a backup copy. Read your Windows or backup software documentation for more information.

If VBS.Confi has executed 11 times, and the system was subsequently restarted, it may have deleted the files. In this case, it is possible that you will no longer be able to start Windows, and it will be necessary to either restore system files from a backup copy, or to re-install the operating system.

Once you have replaced the registry with a clean copy and restored any missing system files, update the virus definitions and run a full system scan as described in the next section.

If VBS.Confi has not yet executed
If your Symantec antivirus product detects VBS.Confi, delete it. If you suspect that the virus exists on your system, but has not yet executed, follow these steps:

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Run a full system scan and delete all the files detected as VBS.Confi or BAT.Trojan.

For specific details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder ," Article ID: Q263455.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with VBS.Confi or BAT.Trojan, note the path and file name, and then click Delete.
  4. Manually delete other files that the Trojan uses. (These files are not harmful by themselves, and therefore, Symantec antivirus products do not detect them.)
    • If VBS.Confi was detected on a floppy disk (for example, A:\folder.htt), delete the corresponding desktop.ini file (A:\desktop.ini).
    • If VBS.Confi was detected as a file named MSKernel32.con, delete MSKernel.con from the same directory.

Writeup By: Heather Shannon