Trojan.Qhosts - Removal

Removal using the Trojan.Qhosts Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of Trojan.Qhosts. This is the easiest way to remove this threat and should be tried first.

Manual Removal
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. Remove all the entries that the risk added to the hosts file.
3. Reinstall your Symantec antivirus program.
4. Update the virus definitions.
5. Run a full system scan and delete all the files detected.
6. Delete any values added to the registry.
7. Reset the Internet Explorer search page.
8. Extract and restore Windows files.
   

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

1. To disable 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:

• How to disable or enable Windows Me System Restore
• How to turn off or turn on Windows XP System Restore

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, reenable 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. To remove all the entries that the risk added to the hosts file

1. Navigate to the following location:
   
   
   • Windows 95/98/Me:
     %Windir%
   • Windows NT/2000/XP:
     %Windir%\System32\drivers\etc
     
     Notes:
   • The location of the hosts file may vary and some computers may not have this file. There may also be multiple copies of this file in different locations. If the file is not located in these folders, search your disk drives for the hosts file, and then complete the following steps for each instance found.
   • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows (Windows 95/98/Me/XP) or C:\Winnt (Windows NT/2000).
     
     
2. Double-click the hosts file.
3. If necessary, deselect the "Always use this program to open this program" check box.
4. Scroll through the list of programs and double-click Notepad.
5. When the file opens, delete all the entries in the Hosts file except for the following line:
   
   127.0.0.1     localhost
   
   
6. Close Notepad and save your changes when prompted.

3. To reinstall your Symantec antivirus program
As this risk attempts to remove the files and registry subkeys that your Symantec antivirus program uses, you may need to reinstall the program. If your Symantec antivirus program is not working properly, uninstall, and then reinstall it.

4. To update 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 document: Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. 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 document: Virus Definitions (Intelligent Updater).
  
  The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions. For detailed instructions read the document: How to update virus definition files using the Intelligent Updater.

5. To scan for and delete the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document: How to configure Norton AntiVirus to scan all files.
   • For Symantec AntiVirus Enterprise products: Read the document: How to verify that a Symantec Corporate antivirus product is set to scan all files.
2. Run a full system scan.
3. If any files are detected, click Delete.

Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode. Once you have restarted in Safe mode, run the scan again.

After the files are deleted, restart the computer in Normal mode and proceed with the next section.

Warning messages may be displayed when the computer is restarted, since the threat may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

Title: [File path]
Message body: Windows cannot find [file name]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.


6. To delete the value from the registry
Important: 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 subkeys only. For instructions refer to the document: How to make a backup of the Windows registry.

1. Click Start > Run.
2. Type regedit
3. Click OK.
   
   Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.
   
   
4. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VxD\MSTCP
   
   Note: This key may not exist on Windows XP computers.
   
   
5. In the right pane, delete the values:
   
   "EnableDNS" = "1"
   "NameServer" = "[IP address specified in the batch file]"
   "HostName" = "host"
   "Domain" = "mydomain.com"
   
   
6. Navigate to the subkey:
   
   HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
   
   
7. In the right pane, delete the values:
   
   "ProxyEnable"="0"
   "MigrateProxy"="0"
   
   
8. Navigate to the keys:
   
   HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Tcpip\Parameters\
   Interfaces\Windows
   HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\Tcpip\Parameters\
   Interfaces\Windows
   
   
9. In the right pane, delete the value:
   
   "r0x" = "your s0x"
   
   
10. Navigate to the keys:
    
    HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Tcpip\Parameters
    HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\Tcpip\Parameters
    
    
11. Modify the value:
    
    "DataBasePath" = "%SystemRoot%\help"
    
    to:
    
    "DataBasePath" = "%SystemRoot%\System32\drivers\etc"
    
    
12. Navigate to the keys:
    
    HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Tcpip\Parameters\
    Interfaces
    HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\Tcpip\Parameters\
    Interfaces
    
    
13. For each subkey, restore the value:
    
    "NameServer" = "[IP address specified in the batch file]"
    
    Note: The default for many configurations is an empty string.
    
    
14. Exit the registry Editor.

7. To reset the Internet Explorer search page
Follow the instructions for your version of Windows.

Windows 98/Me/2000

1. Start Microsoft Internet Explorer.
2. Click the Search button on the toolbar.
3. In the Search pane, click Customize.
4. Click Reset.
5. Click Autosearch Settings.
6. Select a search site from the drop-down list, and then click OK.
7. Click OK.

Windows XP
Because Windows XP is set by default to use animated characters in the search, how you do this can vary. Read all the instructions before you start.

1. Start Microsoft Internet Explorer.
2. Click the Search button on the toolbar.
3. Do one of the following:
   • If the pane that opens looks similar to the following picture, click the word Customize and proceed to step h:
     
     
     
     
     
   • If the pane that opens has the words "Search Companion" at the top, and the center looks similar to the following picture, click the Change preferences link and proceed with step d.
     
     
     
     
     
4. Click the Change Internet search behavior link.
5. Under "Internet Search Behavior," click With Classic Internet Search.
6. Click OK. Then close Internet Explorer. (Close the program for the change to take effect.)
7. Start Internet Explorer. When the search pane opens, it should look similar to the following picture:
   
   
   
   
   
   Click the word Customize, and then proceed with the next step.
   
   
8. In the Search pane, click Customize.
9. Click Reset.
10. Click Autosearch Settings.
11. Select a search site from the drop-down list, and then click OK.
12. Click OK.
13. Do one of the following:
    • If you were using (or want to continue using) the "Classic Internet Search" panel, stop here (or proceed with the next section).
    • If you want to go back to the "Search Companion" search (it usually has an animated character at the button), proceed with step n.
      
      
14. Click the word Customize again.
15. In the "Customize Search Settings" window, click Use Search Companion > OK.
16. Close Internet Explorer. The next time you open it, it will again use the Search Companion.

8. To reinstall Windows Automatic Update
The threat deletes a service relating to Windows Automatic Update. As a result of this it may be necessary to reinstall Automatic Update. The following document provides general instructions on how to do this. This information is provided for your convenience. The exact steps may vary slightly depending on the configuration of your operation system, the location of the files, and so on. For additional information, read the Help files, contact Microsoft, or refer to the following Windows documentation:

The Microsoft Knowledge Base article: Procedure to manually Re-Install Automatic Update Client for Windows Server Updates Services, WSUS.

Technical Details