W32.Sasser.Worm - Removal

Before you begin:
If you are running Windows 2000 or XP, and have not yet done so, you must patch for the vulnerability described in Microsoft Security Bulletin MS04-011. If you do not, it is likely that your computer will continue to be reinfected.

What to do if the computer shuts down before you can patch or get the tool
This threat can cause Windows to keep shutting down and restarting. This can prevent you from installing the Microsoft patch or downloading the tool described below.

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Notes:
• You may have to try this several times, as you only have about 20 seconds to do steps 3 to 6.
• This will not work on Windows 2000.

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To prevent the shut down, do the following:

1. Disconnect the computer from the network/Internet connection. (Disconnect the cable if necessary.)
2. Restart the computer.
3. As soon as Windows opens and you see the Windows desktop, click Start > Run.
4. Type:
   
   cmd
   
   and press Enter.
   
   
5. Type:
   
   shutdown -i
   
   and press Enter.
   
   
6. In the Remote Shutdown Dialog that opens, do the following:
   
   1. Click Add, type your computer name into the Add Computers dialog box, and then click OK.
   2. In the "Display warning for" field, type 9999.
   3. Type the following text in the Comment box:
      
      Delay Lsass.exe shutdown.
      
      
   4. Click OK.
      
      
7. Reconnect the network/Internet connection.
8. Connect to the Internet, and get the patch. Then continue with the steps described below.

When you have patched your computer and removed the threat, you can re-enable the 20 second default warning if you wish.


Removal using the W32.Sasser Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of W32.Sasser.Worm. Use this tool first, as it is the easiest way to remove this threat.

Manual Removal
The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. End the malicious process (Windows NT/2000/XP).
2. Disable System Restore (Windows XP).
3. Update the virus definitions.
4. Run a full system scan and delete all the files detected as W32.Sasser.Worm.
5. Reverse the change made to the registry.
   

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

1. To end the malicious process
On Windows NT/2000/XP computers, you must first end the malicious process. Follow these instructions:

1. Press Ctrl+Alt+Delete once.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to alphabetically sort the processes.
5. Scroll through the list and look for the following processes:
   • avserve.exe
   • any process with a name consisting of four or five digits, followed by _up.exe (for example, 74354_up.exe).
6. If you find any such process, click it, and then click End Process.
7. Exit the Task Manager.
   

2. To disable System Restore (Windows XP)
If you are running Windows XP, we recommend that you temporarily turn off System Restore. Windows 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 "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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3. 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 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.

4. 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 as infected with W32.Sasser.Worm, click Delete.

5. To reverse the change 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. 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_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   
4. In the right pane, delete the value:
   
   "avserve.exe"="%Windir%\avserve.exe"
   
   
5. Exit the Registry Editor.

Technical Details