W32.Datom.Worm

SUMMARY

Due to a decreased rate of submissions, Symantec Security Response has downgraded the threat level of this worm from Category 3 to Category 2 as of May 5, 2003.

W32.Datom.Worm is a worm that spreads through open shares. This worm does not contain a damaging payload.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) July 8, 2002
• Virus Definitions (Intelligent Updater) July 8, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: More than 1000
• Number of Sites: More than 10
• Geographical Distribution: Medium
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Low

Distribution

• Distribution Level: High
• Shared Drives: Spreads across open shares

TECHNICAL DETAILS

W32.Datom.Worm exists as three files:

• Msvxd.exe
• Msvxd16.dll
• Msvxd32.dll

These files are located in the %Windir% folder.

NOTE: %Windir% is a variable. The worm locates the Windows main installation folder (by default this is C:Windows or C:Winnt) and copies itself to that location.

The tasks in each file have likely been separated in an attempt to avoid heuristic detection:

• Msvxd.exe simply runs Msvxd16.dll.
• Msvxd16.dll adds a reference to Msvxd.exe to the registry and then runs Msvxd32.dll.
• Msvxd32.dll enumerates network shares and copies all three files to those shares into the %Windir% folder and adds a reference to Msvxd.exe in the Run= line in Win.ini.

Recommendations

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.

REMOVAL

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Restart in Safe mode.
3. Delete the value
   
   MSVXD
   
   from the registry key
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
4. Delete the Run= line in the Win.ini file if it refers to Msvxd.exe
   
5. Run a full system scan, and delete all files that are detected as W32.Datom.Worm.

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

To obtain the most recent virus definitions:
There are two ways to do this:

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and 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 have undergone full quality assurance testing by Symantec Security Response. They 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 restart in Safe mode:

1. Shut down the computer, turn off the power, and wait 30 seconds.
2. Restart the computer in Safe mode. All Windows 32-bit operating systems except Windows NT can be restarted in Safe mode. For instructions on how to do this, read the document How to start the computer in Safe Mode.

To remove the reference from the Win.ini file:

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:WindowsRecent 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:WindowsRecent, 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:windowswin.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 the line that begins with
   
   run=
   
4. If the run= line refers to Msvxd.exe, select the entire line and delete it.
5. Click File, and click Save.
6. Click File, and click Exit.

To remove the value from 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 following key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the following value:
   
   MSVXD
   
5. Click Registry, and click Exit.

To scan for and delete the infected files:

1. Start your Symantec antivirus software, 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 by W32.Datom.Worm, click Delete.