NOTE: Due to a decreased rate of submissions, Symantec Security Response has downgraded this threat from Category 3 to Category 2 as of June 13, 2003.
W32.Opaserv.Worm is a network-aware worm that attempts to replicate across open network shares. It copies itself to the remote computer as a file named Scrsvr.exe. This worm also attempts to download updates from www.opasoft.com, although the site may have already been shut down. Indicators of infection include:
The existence of the files Scrsin.dat and Scrsout.dat in the root of drive C. This indicates a local infection (that is, the worm was executed on the local computer).
The existence of the Tmp.ini file in the root of drive C. This indicates a remote infection (that is, the computer was infected by a remote host).
The registry key HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\Current Version\Run contains the string value ScrSvr or ScrSvrOld, which is set to c:\tmp.ini.
NOTE: 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 before attempting to remove this worm. If you have shared files or folders, these must be disabled. 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
NOTE: %windir% is a variable. The worm locates the Windows installation folder (by default this is C:\Windows or C:\Winnt) and uses that as a destination folder.
After the worm checks the registry values and the location from which the worm is executing, the worm checks to make sure that only one instance of the worm is running in memory by creating a mutex with the name ScrSvr31415.
If it is not already executing, the worm registers itself as a process under Windows 95/98/Me. Under Windows NT/2000/XP it elevates the priority of the worm process.
The worm then inventories the network looking for "C\" shares. For each share that it finds, it copies itself to C\Windows\Scrsvr.exe.
The 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,
So that Windows 95/98/Me computers will run the worm each time that you start Windows, the worm modifies the[windows]section of the C:\Windows\Win.ini file by adding the line
run= c:\ScrSvr.exe
NOTES:
The worm modifies the file C:\Windows\Win.ini before it copies itself as %windir%\ScrSvr.exe. Therefore, Symantec antivirus products will find and delete %windir%\ScrSvr.exe after the system has been altered, but not before it modifies the Win.ini file. As a result, when you restart the computer, you may see a message that ScrSvr.exe cannot be found. To fix this, remove the line that the worm added.
The worm is apparently coded to add this line to the Win.ini:
run= c:\tmp.ini
However, in actual infections or detections, the worm is adding the line run= c:\ScrSvr.exe.
It also creates C:\Tmp.ini, which contains the text
run= c:\windows\scrsvr.exe
The worm also appears to be able to update itself by reading files from a Web site whose URL is hardcoded within the worm. It also attempts to download an update named Scrupd.exe.
Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":
Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
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.
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.
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:
Disconnect from the network if connected.
Update the virus definitions.
Run a full system scan, and delete all files that are detected as W32.Opaserv.Worm
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.
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
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:
Start your Symantec antivirus program, and make sure that it is configured to scan all files.
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.
Click Start, and click Run. The Run dialog box appears.
Type regedit and then click OK. The Registry Editor opens.
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.
Click Start, and click Run.
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.
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
Select the entire line. Be sure that you have not selected any other text in the file, and then press Delete.
Click File, and click Save.
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.
Additional information:
If you are on a network, have a full time connection to the Internet such as DSL or Cable modem, or often leave a dial-up connection open for extended periods, we strongly recommend the installation of a firewall for additional protection. For information on Symantec firewall products, go to:
