Discovered: October 03, 2003
Updated: December 14, 2005 12:00:00 AM
Type: Removal Information
Symantec Security Response has developed a removal tool to clean infections of:
What the tool does
The Trojan.Qhosts Removal Tool does the following:
Terminates the Trojan.Qhosts viral processes.
Deletes the Trojan.Qhosts files.
Deletes most of the registry values that the worm added.
Note: The tool does not delete the values:
"Use Search Asst"="no"
"Search Page"="http:/ /www.google.com"
"Search Bar"="http:/ /www.google.com/ie"
from the registry key:
because these are custom settings and it is not possible to know what your previous setting was. All of these settings can be reset from within the program. Read you Internet Explorer documentation for instructions.
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 Runs the tool in silent mode.
/LOG=[PATH NAME] Creates a log file where [PATH NAME] is the location in which the log will be placed. By default, this switch creates the log file, FixQhost.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 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 Prevents the scanning of the file system.
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.
The /EXCLUDE switch will only work with one path, not multiple paths. An alternative is the /NOFILESCAN switch, followed by a manual scan with your Symantec antivirus product. This allows the tool to alter the registry. Then, scan the computer using the current virus definitions.
The following is an example command line that can be used to exclude a single drive:
"C:\Documents and Settings\user1\Desktop\FixQhost.exe" /EXCLUDE=M:\ /LOG=c:\FixQhost.txt
As an alternative, the following command line below will skip scanning the file system, but will repair the modifications to the registry. You should then run a regular scan of the system with the proper exclusions:
"C:\Documents and Settings\user1\Desktop\FixQhost.exe" /NOFILESCAN /LOG=c:\FixQhost.txt
(The name of the log file can be whatever you choose.)
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 FixQhost.exe file from: http://www.symantec.com/avcenter/FixQhost.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.
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.
Note: This is done as a precaution to prevent the worm from accidentally being restored at a later date or from being detected by a scan. However, due to the changes that the worm makes to the registry, you may not be able to do this at this time. If you cannot, skip this for now. We recommend, however, that you do so after you have restored access to your system; doing so, will empty the System Restore folder and prevent possible future problems.
Double-click the FixQhost.exe 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.
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 Trojan.Qhosts 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
FixQhost.exe is digitally signed. Symantec recommends that you only use copies of FixQhost.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 FixQhost.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 FixQhost.exe and Chktrust.exe are stored, and then type: chktrust -i FixQhost.exe.
For example, if you saved the file to the C:\Downloads folder, you would enter the following commands:
chktrust -i FixQhost.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 "Trojan.Qhosts Removal Tool" signed on 10/03/2003 10:33 AM 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 computer becomes infected with a virus, worm, or Trojan, 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.