Discovered: October 29, 2003
Updated: October 18, 2006 12:00:00 AM
Type: Removal Information

Symantec Security Response has developed a removal tool to clean the infections of the following W32.Sober variants:

Note: W32.Sober.gen is a generic detection that detects variants of W32.Sober. If your computer is detected as infected with W32.Sober.gen, download and run the tool. In most cases, the tool will be able to remove the infection.

What the tool does

The W32.Sober Removal Tool does the following:
Terminates the W32.Sober viral processes.
Deletes the W32.Sober files.
Deletes the dropped files.
Deletes the registry values that the worm added.
Command-line switches available with this tool

Switch Description
/HELP, /H, /? Displays the help message.
/NOFIXREG Disables the registry repair. (We do not recommend using this switch.)
/SILENT, /S Enables the silent mode.
/LOG=[PATH NAME] Creates a log file where [PATH NAME] is the location in which to store the tool's output. By default, this switch creates the log file, FxSobr.log, within the same folder from which the removal tool was executed.
/MAPPED Scans the mapped network drives. (We do not recommend using this switch. Refer to the Notes below.)
/START Forces the tool to immediately start scanning.
/EXCLUDE=[PATH] Excludes the specified [PATH] from scanning. (We do not recommend using this switch.)
/NOFILESCAN Prevents scanning of the file system.

Symantec Security Response strongly recommends that you not use the /NOFIXREG switch when running this removal tool for the first time. If the removal tool is run using this switch, you will not be able to remove the registry keys associated with this worm by running the tool again.

Using the /MAPPED switch does not ensure the complete removal of the virus on the remote computer, because:
Scanning the mapped drives scans the mapped folders only. This action may not include all the folders on the remote computer, leading to missed detections.
If a viral file is detected on the mapped drive, the removal will fail if a program on the remote computer uses this file.

For these reasons, run the tool on every computer.

Obtaining and running the tool

Note: You need administrative rights to run this tool on Windows NT 4.0, Windows 2000, or Windows XP.

WARNING: For network administrators. If you are running MS Exchange 2000 Server, we recommend that you exclude the M drive from the scan by running the tool from a command line with the Exclude switch. For more information, read the Microsoft knowledge base article, XADM: Do Not Back Up or Scan Exchange 2000 Drive M (Article 298924).

Download the FixSbr.exe file from:
Save the file to a convenient location, such as your downloads folder or the Windows Desktop (or removable media that is known to be uninfected, if possible).
To check the authenticity of the digital signature, refer to the section, "Digital signature."
Close all the running programs before running the tool.
If you are on a network or you have a full-time connection to the Internet, disconnect the computer from the network and the Internet.
If you are running Windows Me or XP, then disable System Restore. Refer to the section, "System Restore option in Windows Me/XP," for additional details.

CAUTION: If you are running Windows Me/XP, we strongly recommend that you do not skip this step. The removal procedure may be unsuccessful if Windows Me/XP System Restore is not disabled, because Windows prevents outside programs from modifying System Restore.

Double-click the FixSbr.exe file to start the removal tool.
Click Start to begin the process, and then allow the tool to run.

Note: If, when running the tool, you see a message that the tool was not able to remove one or more files, run the tool in Safe mode. Shut down the computer, turn off the power, and wait 30 seconds. Restart the computer in Safe mode and run the tool again. All the Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions on restarting the computer in Safe mode, read the document, How to start the computer in Safe Mode.

Restart the computer.
Run the removal tool again to ensure that the system is clean.
If you are running Windows Me/XP, then re-enable System Restore.

Note: Before continuing to the next step, it may be necessary to reinstall LiveUpdate as some variants, like W32.Sober.O@mm and W32.Sober.X@mm, specifically target Symantec LiveUpdate and attempts to delete/overwrite various files associated with this product. In order to reinstall LiveUpdate, please follow these instructions:

To reinstall the current version of LiveUpdate
Click download LiveUpdate.

Note: If you are not reading this Web page on the computer that is getting the error notice, the address for downloading the file is:

If necessary, you can type this address into the address bar of the problem computer. Changes to the Hosts file will not stop you from getting to this site.

Save the file to the Windows desktop.
Double-click the lusetup.exe icon on the desktop to install LiveUpdate.

Run LiveUpdate to make sure that you are using the most current virus definitions.

When the tool has finished running, you will see a message indicating whether W32.Sober infected the computer. In the case of a worm removal, the program displays the following results:
Total number of the scanned files
Number of deleted files
Number of terminated viral processes
Number of fixed registry entries

Digital signature
FixSbr.exe is digitally signed. Symantec recommends that you only use copies of FixSbr.exe that have been directly downloaded from the Symantec Security Response Web site. To check the authenticity of the digital signature, follow these steps:
Go to
Download and save the Chktrust.exe file to the same folder in which you saved the removal tool.

Note: Most of the following steps are done at a command prompt. If you downloaded the removal tool to the Windows desktop, it will be easier if you first move the tool to the root of the C drive. Then save the Chktrust.exe file to the root of C as well.

(Step 3 to assume that both the removal tool and Chktrust.exe are in the root of the C drive.)

Click Start > Run.
Type one of the following:
Windows 95/98/Me:


Windows NT/2000/XP:


Click OK.
In the command window, type the following, pressing Enter after typing each line:

cdcd downloads
chktrust -i FixSbr.exe

You should see one of the following messages, depending on your operating system:

Windows XP SP2:
The Trust Validation Utility window will appear.

Under Publisher, click the Symantec Corporation link. The Digital Signature Details appears.
Verify the contents of the following fields to ensure that the tool is authentic:

Name: Symantec Corporation
Signing Time: Tuesday, November 22, 2005 03:27:19 PM

All other operating systems:
You should see the following message:

Do you want to install and run "W32.Sober Removal Tool" signed on 11/22/2005 03:47:28 PM and distributed by Symantec Corporation?

The date and time in the digital signature above are based on Pacific time. They will be adjusted your computer's time zone and Regional Options settings.
If you are using Daylight Saving time, the displayed time will be exactly one hour earlier.
If this dialog box does not appear, there are two possible reasons:
The tool is not from Symantec: Unless you are sure that the tool is legitimate and that you downloaded it from the legitimate Symantec Web site, you should not run it.
The tool is from Symantec and is legitimate: However, your operating system was previously instructed to always trust content from Symantec. For information on this and on how to view the confirmation dialog again, read the document: How to restore the Publisher Authenticity confirmation dialog box.

Click Yes or Run to close the dialog box.
Type exit, and then press Enter. (This will close the MS-DOS session.)

System Restore option in Windows Me/XP
Users of Windows Me and Windows XP should 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, in some cases, online scanners may detect a threat in the System Restore folder even though you scanned your computer with an antivirus program and did not find any infected files.

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

For additional information and an alternative to disabling Windows Me System Restore, read the Microsoft Knowledge Base article, Antivirus Tools Cannot Clean Infected Files in the _Restore Folder, Article: Q263455.

How to run the tool from a floppy disk
Insert the floppy disk, which contains the FixSbr.exe file, in the floppy disk drive.
Click Start, and then click Run.
Type the following:


and then click OK:

There are no spaces in the command, a:\FixSbr.exe.
If you are using Windows Me and System Restore remains enabled, you will see a warning message. You can choose to run the removal tool with the System Restore option enabled or exit the removal tool.

Click Start to begin the process, and then allow the tool to run.
If you are using Windows Me, then re-enable System Restore.