W32.Opaserv.Worm - Removal

IMPORTANT - READ THIS FIRST:

• This worm uses a security vulnerability in Microsoft Windows 95/98/Me. It sends single character passwords to network shares to get access to Windows 95/98/Me file shares without knowing the entire password assigned to the shares. The affected systems include Windows 95, 98, and Me.
  
  A patch for computers running these operating systems can be found at http://www.microsoft.com/technet/security/bulletin/MS00-072.asp. If you have not already done so, you must obtain and install the patch to prevent future infections.
  
• If you are on a network, or have a full time connection to the Internet such as DSL or Cable modem, you must disconnect the computer from the network and the Internet. Disable sharing before reconnecting computers to the network or to the internet. Because this worm spreads by using shared folders on networked computers, to ensure that the worm does not reinfect the computer after it has been removed, you must remove all shares, clean all computers on the network, patch all systems, and update definitions on all computers before you reconnect to the network or reenable shares.
• For instructions on how to do this,see your Windows documentation or the document How to configure shared Windows folders for maximum network protection.
• If you are removing an infection on a network, make sure any shares are disabled before doing so.

Removal using the W32.Opaserv.Worm Removal Tool
This is the easiest way to remove this threat. Symantec Security Response has created a W32.Opaserv.Worm Removal Tool. Click here to obtain the tool.
 
Manual Removal
As an alternative to using the removal tool, you can remove this threat manually. Here are the major steps:

1. Disconnect from the network if connected.
2. Update the virus definitions.
3. Run a full system scan, and delete all files that are detected as W32.Opaserv.Worm
4. Delete the values
   
   ScrSvr %windir%\ScrSvr.exe
   
   and
   
   ScrSvrOld <original worm name>
   
   from the registry key
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   
5. (Windows 95/98/Me only ) Delete the line
   
   run= c:\ScrSvr.exe
   
   or
   
   run= c:\tmp.ini
   
   from the C:\Windows\Win.ini.
   

For details on how to do this, read the following instructions.

To disconnect from the network:
If you are on a network, or have a full time connection to the Internet such as DSL or Cable modem, you must disconnect the computer from the network and the Internet. Disable sharing before reconnecting computers to the network or to the internet. Because this worm spreads by using shared folders on networked computers, to ensure that the worm does not reinfect the computer after it has been removed, you must remove all shares, clean all computers on the network, patch all systems, and update definitions on all computers before you reconnect to the network or reenable shares.

IMPORTANT:

• Do not skip this step. You must disconnect from the network before attempting to remove this worm.
• For additional information on file sharing, read your Windows documentation or the document How to configure shared Windows folders for maximum network protection.
• When you have finished the removal procedure, if you decide to reenable file sharing, Symantec suggests that you do not share the root of drive C. Share specific folders instead. These shares must be password-protected with a secure password. Do not use a blank password.
  
  Also, before doing so, if you are using Windows 95/98/Me, you must download and install the Microsoft patch from
  
  http://www.microsoft.com/technet/security/bulletin/MS00-072.asp

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
• Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
  
  Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

To scan for and delete the infected files:

1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
   • Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec enterprise antivirus products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
2. Run a full system scan.
3. If any files are detected as infected with W32.Opaserv.Worm, click Delete.

To remove the value that the worm added to the registry:

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the key
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   
4. In the right pane, delete these value:
   
   ScrSvr %windir%\ScrSvr.exe
   
   ScrSvrOld <original worm name>
   
5. Exit the Registry Editor.

To delete the line that the worm added to the Win.ini file:
This is necessary only on Windows 95/98/Me-based computers.

NOTE: (For Windows Me users only) Due to the file-protection process in Windows Me, a backup copy of the file that you are about to edit exists in the C:\Windows\Recent folder. Symantec recommends that you delete this file before you continue with the steps in this section. To do this using Windows Explorer, go to C:\Windows\Recent, and in the right pane select the Win.ini file and delete it. It will be regenerated as a copy of the file that you are about to edit when you save your changes to that file.

1. Click Start, and click Run.
2. Type the following, and then click OK.
   
   edit c:\windows\win.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
3. In the [windows] section of the file, look for an entry similar to either (or both) of the following:
   
   run= c:\ScrSvr.exe
   
   run= c:\tmp.ini
   
4. Select the entire line. Be sure that you have not selected any other text in the file, and then press Delete.
5. Click File, and click Save.
6. Click File, and click Exit.

NOTE: There have been several reports of infections by this worm in which the worm itself was infected with a virus that then also spread to the infected computer. For this reason, we suggest that after you have finished removing W32.Opaserv.Worm, that you run a full system scan. If any files are detected as infected with a different threat, go to http://securityresponse.symantec.com/avcenter/vinfodb.html, enter the name of the detection in the field, and then click search. Open the document if one is found and follow any removal instructions.

Technical Details