Backdoor.Exdis - 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. Update the virus definitions.
3. Restart the computer in Safe mode or VGA mode.
4. Reverse the changes made to the registry.
5. Scan for and delete files detected as Backdoor.Exdis.

For 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:

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

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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.

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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. Reversing the changes made to the registry

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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.

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1. On the Desktop, double-click My Computer.
   
   
   
2. Make sure that Windows is showing file extentions. In order to check this, do the following:
   
   1. Click the View menu (Windows 95/98/NT) or the Tools menu (Windows Me/2000/XP), and then click Options or "Folder options."
   2. Click the View tab.
   3. Click the Restore Defaults button.
   4. Click OK.
      
      
3. Navigate to the following file, depending on your operating system:
   
   • Windows 95/98/Me/XP:
     C:\Windows\regedit.exe
     
     
   • Windows NT/2000:
     C:\Winnt\regedit.exe
     
     
4. Right-click on regedit.exe and select Rename.
   
   
5. Type the following:
   
   regedit.com
   
   
   and then press Enter.
   
   
6. Double click regedit.com.
   
   
7. Navigate to and select the key:
   
   HKEY_CLASSES_ROOT\exefile\shell\open\command
   
   
8. In the right pane, double-click the (Default) value.
   
   
9. Delete the current value data, and then type:
   
   "%1" %*
   
   That is, type the characters: quote-percent-one-quote-space-percent-asterisk.
   
   
10. The next few steps depend on the operating system you are running.
    
    • If you are running Windows 95/98/Me, skip to step m.
    • Windows 2000/XP/NT only
      Navigate to each of these keys:
      
      HKEY_LOCAL_MACHINE\System\ControlSet001\Services
      HKEY_LOCAL_MACHINE\System\ControlSet002\Services
      HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services
      
      
11. From each one, delete any of these subkeys that you find:
    
    xd2s
    xad2
    xadx
    xadz
    
    
12. If none of these subkeys are found, the Trojan may be using a different service name. In which case, search the registry for references to the Trojan file:
    
    1. Click Edit > Find.
       
       
    2. In the "Find what" box, type:
       
       ImagePath
       
       
    3. In the "Look at" section, make sure that the Values check box is selected. Deselect the Keys or Data check boxes.
       
       
    4. Click Find Next.
       
       
    5. Allow the search to run until it finds an entry similar to the following:
       
       ImagePath = "%Windir%\<the Trojan file name>"
       
       in a registry key similar to the following:
       
       HKEY_LOCAL_MACHINE\System\<key name>\Services\<any service name>
       
       
    6. If you find such a key, delete it. For example, if you find an entry similar to:
       
       ImagePath = "C:\WINNT\wxyabc.exe"
       
       in the key:
       
       HKEY_LOCAL_MACHINE\System\ControlSet001\Services\xabc
       
       then delete the entire subkey "xabc."
       
       
13. Exit the Registry Editor.
    
    
14. Repeat steps c through e to change regedit.com back to regedit.exe.

5. To scan for and delete files detected as Backdoor.Exdis

1. On your Desktop, double-click My Computer.
2. Right-click your C:\ drive and select one of the following:
   • For Norton AntiVirus consumer products: "Scan with Norton Antivirus"
   • For Symantec AntiVirus Enterprise products: "Scan for Viruses..."
3. If any files are detected as infected with Backdoor.Exdis, click Delete.

Technical Details