W32.Valla.2048

SUMMARY

The W32.Valla.2048 virus infects Win32 files by appending the virus code to the host. The infected files increase in size by 2,048 bytes.

Protection

• Virus Definitions (LiveUpdate™ Weekly) November 24, 2002
• Virus Definitions (Intelligent Updater) November 24, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low
• Modifies Files: Win32 files

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When W32.Valla.2048 is executed, it infects Win32 executable files in the %Windir% and %System% folders.

NOTES:

• %Windir% is a variable. The virus locates the Windows installation folder (by default this is C:Windows or C:Winnt) and infects files in that location.
• %System% is a variable. The virus locates the System folder and infects files in that location. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).

This virus infects files by adding a new section named "XOR" at the end of the last section of the host, and it appends the virus code to the host. W32.Valla.2048 has an infection size of 2,048 bytes and is a direct file infector.

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

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Disable System Restore (Windows Me/XP).
2. Update the virus definitions.
3. Restart the computer in Safe mode or VGA mode.
4. Run a full system scan and repair all the files detected as W32.Valla.2048.
5. Run the Norton AntiVirus DOS scanner (Windows 95/98/Me), if necessary. (Consumer products only).

For specific details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you 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 virus, worm, or Trojan infects a computer, System Restore may back 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 of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

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, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Restarting the computer in Safe mode or VGA mode
Shut down the computer and turn off the power. Wait for at least 30 seconds, then restart the computer in Safe mode or VGA mode.

• For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, refer to the document, "How to start the computer in Safe Mode."
• For Windows NT 4 users, restart the computer in VGA mode.

4. Scanning for and repairing the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that 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.Valla.2048, click Repair.

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Note: In some cases, depending on which files have been infected, Norton AntiVirus may not be able to repair all the infected files while in Windows. In such cases, you will need to run the Norton AntiVirus DOS scanner. If Norton AntiVirus was able to repair all the infected files, you will not need to run the DOS scanner.

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5. Running the Norton AntiVirus DOS scanner (Windows 9x)

1. Restart the computer in MS-DOS mode by doing the following:
   
   Windows 95
   Restart the computer and watch the screen. When you see "Starting Windows 95," press F8.
   
   Windows 98
   Restart the computer and immediately press and hold down the Ctrl key until the Windows 98 startup menu appears.
   
   
2. Select "Safe Mode Command Prompt Only" from the startup menu, and then press Enter.
3. At the C:> prompt, type the following command:
   
   dir /s /b avdx.exe
   
   Then press Enter.
   
   This displays the path to the Norton AntiVirus (NAV) DOS scanner. If Norton AntiVirus is installed to a different drive, first change to the root of that particular drive. The default is C:Program FilesNorton AntiVirus.
   
   
4. Change to the folder that contains Navdx.exe. Use short file names. For example, if Norton AntiVirus is installed in C:Program FilesNorton AntiVirus, type:
   
   cd progra~1 orton~1
   
   
5. Type the following command:
   
   navdx /a /doallfiles /prompt [Enter]
   
   

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   Note: This scan could take several hours or more on some computers. Do not stop the scan once it has started.

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6. Press R)epair for each infected file. If Norton AntiVirus cannot repair an infected file, you will see the message, "Unable to repair the file." In most cases, you should choose D)elete, unless you are sure that the file is not actually infected.
   
   
7. Restart the computer.