Symantec United States
global sites
products and services
security response
about symantec

© 1995-2004 Symantec Corporation.
All rights reserved.
Legal Notices
Privacy Policy

security response


Discovered on: October 13, 2003
Last Updated on: October 20, 2003 06:27:15 PM

Trojan.Bootconf is a Trojan Horse that modifies the TCP/IP settings to point to a different DNS server. It will also change your home page and search page in Internet Explorer to connect to

Trojan.Bootconf is written in Microsoft Visual C++.

Note: Virus definitions dated prior to October 14, 2003 may detect this as Trojan.Qhosts.A or Trojan.Qhosts.B.

Also Known As: Trojan.Qhosts.A, Trojan.Qhosts.B, TrojanClicker.Win32.Qhost.a [KAV]
Type: Trojan Horse
Infection Length: varies, known variants are 53,248 or 57,344 bytes
Systems Affected: Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows XP
Systems Not Affected: DOS, Linux, Macintosh, Microsoft IIS, OS/2, UNIX, Windows 3.x

  • Virus Definitions (Intelligent Updater) *
  • October 13, 2003

  • Virus Definitions (LiveUpdate™) **
  • October 15, 2003


    Intelligent Updater definitions are released daily, but require manual download and installation.
    Click here to download manually.


    LiveUpdate virus definitions are usually released every Wednesday.
    Click here for instructions on using LiveUpdate.

    threat assessment


    Threat Metrics

    Low Low Low




    technical details

    When the Trojan.Bootconf is executed, it performs the following actions:

    1. Adds the address entry:

      <an invalid IP address>

      to the HOSTS file, disabling access to this site.

    2. Creates a non-viral file in different locations, depending on the variant. Known variants have installed this file in %Windir%\Web\Oslogo.bmp and %Windir%\default.css.

      Note: %Windir% is a variable. The Trojan locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt), and creates a file in that directory or in a subdirectory.

    3. Adds the values:
      • "Search" = <encoded URL>
      • "SearchURL" = <encoded URL>

        in the registry key:

        HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer

        The URL varies, and may be one of:
      • http:// %6f%75%74%2e%74%72%75%65%2d%63%6f%75%6e%74%65%72%2e%63%6f%6d/%61/?%33%34%34%30%31%32
      • http:// %77%77%77%2e%63%6f%6f%6c%77%77%77%73%65%61%72%63%68%2e%63%6f%6d/%7a/%61/%78%31%2e%63%67%69?%33%34%34%30%31%32

    4. Adds the values:
      • "SearchAssistant" = <encoded URL>
      • "CustomizeSearch" = <encoded URL>

        in the registry key:

        HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Search

    5. Modifies the values:
      • "Search Page" = <encoded URL>
      • "Default_Search_URL" = <encoded URL>
      • "Search Bar" = <encoded URL>
      • "Default_Page_URL" = <encoded URL>
      • "Start Page" = <encoded URL>

        in the registry key:

        HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main

    6. Modifies the values:
      • "User Stylesheet" = <the filename from step #2>
      • "Use My Stylesheet" = "1"

        in the registry key:

        HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Styles


    Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

    removal instructions

    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. Restart the computer in Safe mode or VGA mode.
    4. Run a full system scan and delete all the files detected as Trojan.Bootconf.
    5. Delete the value that was added to the registry.
    6. Restore Internet Explorer settings.
    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:

    Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

    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. Restarting the computer in Safe mode or VGA mode

    Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.
    • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
    • For Windows NT 4 users, restart the computer in VGA mode.

    4. 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 Trojan.Bootconf, click Delete.

    5. Deleting the value from the registry

    WARNING: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

    1. Click Start, and then click Run. (The Run dialog box appears.)
    2. Type regedit

      Then click OK. (The Registry Editor opens.)

    3. Navigate to the key:

      HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer

    4. In the right pane, delete the values:
      • "Search" = <encoded URL>
      • "SearchURL" = <encoded URL>

    5. Navigate to the key:

      HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Search

    6. In the right pane, delete the values:
      • "SearchAssistant" = <encoded URL>
      • "CustomizeSearch" = <encoded URL>

    7. Exit the Registry Editor.

    6. Restoring the Internet Explorer settings
    Some of the changes that the Trojan makes to the registry will modify some Internet Explorer settings. One of the settings it changes is to the home page.

    To reset the home page:
    1. Start Microsoft Internet Explorer.
    2. Connect to the Internet and go to the page that you want to set as your home page.
    3. Click Tools, and then click Internet Options.
    4. In the Home page section of the General tab, click Use Current, and then click OK.

    If you notice any other problems when you use Internet Explorer, change these settings within the program. See your Internet Explorer documentation for instructions.

    Revision History:

    • October 15, 2003: Renamed to Trojan.Bootconf from Trojan.Qhosts.B.
    • October 14, 2003: Renamed to Trojan.Qhosts.B from Trojan.Qhosts.A.

    Write-up by: Hiroshi Shinotsuka