Discovered: August 18, 2003
Updated: December 12, 2005 12:00:00 AM
Type: Removal Information
Symantec Security Response has developed a removal tool to clean infections of W32.Welchia.Worm, W32.Welchia.B.Worm, W32.Welchia.C.Worm, and W32.Welchia.D.Worm.
What the tool does
The W32.Welchia.Worm Removal Tool does the following:
Terminates the W32.Welchia.Worm (or W32.Welchia.B / W32.Welchia.C / W32.Welchia.D) Worm viral processes.
Deletes the files that the worm added.
Deletes the registry values that the worm added.
Note: Deletion will be performed only if the operating system has not already removed these values upon terminating the viral processes, as mentioned in step 1.
Deletes the services that W32.Welchia.Worm created.
Available command-line switches for this tool
/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, FixWelch.log, in the same folder from which the removal tool was executed.
/MAPPED Scans the mapped network drives. (We do not recommend using this switch. See the following Note.)
/START Forces the tool to immediately start scanning.
/EXCLUDE=[PATH] Excludes the specified [PATH] from scanning. (We do not recommend using this switch.)
/NOFILESCAN Scans the %System%\Wins folder for Dllhost.exe and Svchost.exe only.
Notes: Using the /MAPPED switch does not ensure the complete removal of the virus on the remote computer, because:
The scanning of mapped drives scans only the mapped folders. This may not include all the folders on the remote computer, which can lead 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.
Therefore, you should run the tool on every computer.
Obtaining and running the tool
Note: You must have 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 FixWelch.exe file from: http://www.symantec.com/avcenter/FixWelch.exe.
Save the file to a convenient location, such as your downloads folder or the Windows desktop (or removable media known to be uninfected).
To check the authenticity of the digital signature, refer to the "Digital signature" section later in this writeup.
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 "System Restore option in Windows Me/XP" section later in this writeup for further details.
WARNING: If you are running Windows Me/XP, we strongly recommend that you do not skip this step.
Double-click the FixWelch.exe file to start the removal tool.
Click Start to begin the process, and then allow the tool to run.
If problems occur when running the tool
If the tool fails to run as expected or it reports that it was not able to remove all the files or end all the processes, run the tool again in Safe mode. In this situation, turn off the power, wait 30 seconds, and then restart the computer in Safe mode (Windows 95/98/Me/2000/XP), and then run the tool again. For instructions on restarting the computer in Safe mode, read the document, "How to start the computer in Safe Mode."
Once the tool has run in Safe mode, proceed to step 9.
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.
Run LiveUpdate to make sure that you are using the most current virus definitions.
Note: The removal procedure may not be successful if Windows Me/XP System Restore is not disabled as previously directed, because Windows prevents outside programs from modifying System Restore.
When the tool has finished running, you will see a message indicating whether W32.Welchia.Worm infected the computer. In the case of a removal of the worm, 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.
FixWelch.exe is digitally signed. Symantec recommends that you only use copies of FixWelch.exe, which have been directly downloaded from the Symantec Security Response Web site. To check the authenticity of the digital signature, follow these steps:
Go to http://www.wmsoftware.com/free.htm.
Download and save the chktrust.exe file to the same folder in which you saved FixWelch.exe (for example, C:\Downloads).
Depending on your operating system, do one of the following:
Click Start, point to Programs, and then click MS-DOS Prompt.
Click Start, point to Programs, click Accessories, and then click Command Prompt.
Change to the folder in which FixWelch.exe and Chktrust.exe are stored, and then type: chktrust -i FixWelch.exe.
For example, if you saved the file to the C:\Downloads folder, you would enter the following commands:
chktrust -i FixWelch.exe
Press Enter after typing each command. If the digital signature is valid, you will see the following:
"Do you want to install and run "W32.Welchia Removal Tool" signed on 03/25/04 9:37 PM and distributed by Symantec Corporation?"
The date and time displayed in this dialog box will be adjusted to your time zone, if your computer is not set to the Pacific time zone.
If you are using Daylight Saving time, the time displayed 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 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 has infected a computer, it is possible that System Restore backed 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 to restore an infected file onto 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, see the Microsoft Knowledge Base article, "Anti-Virus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.