Discovered: July 03, 2002
Updated: January 31, 2006 12:00:00 AM
Type: Removal Information

What the tool does
Version 1.0.4 of the The W32.Yaha Removal tool is available for download. This tool will remove the following threats as well as their side effects:


Terminates the viral processes associated with the W32.Yaha variants list above.
Deletes executable files associated with the W32.Yaha variants list above.
Fixes the registry entries associated with the W32.Yaha variants list above.

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, FixYaha.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. See 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.)

NOTE: The use of 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 process might 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, you should run the tool on every computer.

Obtaining and running the tool

IMPORTANT. Read the following Notes before you begin.
You must be logged in as Administrator to run this tool on Windows NT 4.0, Windows 2000, or Windows XP. If you are not sure how to do this, or if you do not have these rights, consult your network administrator or a computer consultant.
If the tool is being used to remove the W32.Yaha.K@mm or W32.Yaha.L@mm infection from a Windows XP computer, you must run the tool in Safe mode.

Download the file from:
Save the file to a convenient location, such as your downloads folder or the Windows desktop (or the 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 if you have a full-time connection to the Internet, disconnect the computer from the network and Internet.
If you are running Windows Me or XP, disable System Restore. Refer to the "System Restore option in Windows Me/XP" section later in this writeup for additional details.

CAUTION: If you are running Windows Me/XP, we strongly recommend that you do not skip this step.

If you are using the tool to remove a W32.Yaha.K@mm or W32.Yaha.L@mm infection from a Windows XP computer, restart the computer in Safe mode. All the Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
Double-click the file to start the removal tool.
Click Start to begin the process, and then allow the tool to run.
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.
Start your Symantec antivirus product and run a full system scan.

NOTE: The removal procedure may not be successful if Windows Me/XP System Restore is not disabled as previously directed, as Windows prevents System Restore from being modified by outside programs. Therefore, the removal tool could fail.

When the tool has finished running, you will see a message indicating whether the computer was infected by W32.Yaha.E@mm/W32.Yaha.F@mm/W32.Yaha.K@mm/W32.Yaha.L@mm. In the case of a worm removal, the program displays the following results:
Total number of the scanned files
Number of the deleted files
Number of the repaired files
Number of the terminated viral processes
Number of the fixed registry entries

Digital signature is digitally signed. Symantec recommends that you only use copies of downloaded directly 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 (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 and Chktrust.exe are stored, and then type:

chktrust -i

For example, if you saved the file to the C:\Downloads folder, you would enter the following commands:

cdcd downloads
chktrust -i

Press Enter after typing each command. If the digital signature is valid, you will see the following:

"Do you want to install and run the "W32.Yaha Fix Tool" signed on 07/31/03 10:46 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
Windows Me and Windows XP users 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. When a computer is infected with a virus, worm, or Trojan, System Restore may be able to back up the virus, worm, or Trojan. By default, Windows prevents System Restore from being modified by outside programs. As a result, there is the possibility of accidentally restoring an infected file, or online scanners detecting the threat in that particular location. 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 disable or enable Windows XP System Restore"
For additional information, as well as 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.

Running the tool from a floppy disk
Insert the floppy disk that contains the file in the floppy disk drive.
Click Start, and then click Run.
Type the following:


then click OK.

There are no spaces in the command a:\
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 to exit the removal tool.
Click Start to begin the process, and then allow the tool to run.
If you are using Windows Me, re-enable System Restore.