Infectionname: Worm Sasser
Type: Worm
Other names: McAfee: W32/Sasser.worm
TrendMicro: WORM_SASSER
Kaspersky Lab: Worm.Win32.Sasser
Sophos: W32/Sasser
Computer Assoc: Win32.Sasser
F-Secure: Sasser
Panda: W32/Sasser.worm
Risk: Medium
Reported by: The [SYP] SaveYourPC Team

What is a Worm?

A computer worm is a self-replicating computer program. It uses a network to send copies of itself to other nodes (computer terminals on the network) and it may do so without any user intervention. Unlike a virus, it does not need to attach itself to an existing program. Worms almost always cause harm to the network, if only by consuming bandwidth, whereas viruses almost always corrupt or modify files on a targeted computer.

How to delete Worm Sasser?

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.

• 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 -a
   
   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 from Symantec

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 are steps to manual remove Worm Sasser.

1. End the malicious process (Windows NT/2000/XP).

2. Disable System Restore (Windows XP).

3. Update the virus definitions of your Anti Virus Software.

4. Run a full system scan and delete all the files detected as Worm Sasser.

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!

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5. Reverse the change made to the registry.

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_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   

4. In the right pane, delete the value:
   
   "avserve.exe"="%Windir%avserve.exe"

    

5. Exit the Registry Editor.