W32.Wilsef

SUMMARY

W32.Wilsef is a simple virus that acts as a backdoor and copies itself to floppy disks as "Doc1.doc.exe."

Protection

• Virus Definitions (LiveUpdate™ Weekly) December 20, 2003
• Virus Definitions (Intelligent Updater) December 18, 2003

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
• Payload Trigger: N/A
• Payload: Opens a backdoor
• Large Scale E-mailing: N/A
• Deletes Files: N/A
• Modifies Files: May overwrite files with a copy of the Trojan.
• Releases Confidential Info: N/A
• Degrades Performance: N/A
• Causes System Instability: N/A
• Compromises Security Settings: N/A

Distribution

• Distribution Level: Low
• Subject of Email: N/A
• Name of Attachment: N/A
• Size of Attachment: N/A
• Ports: N/A
• Shared Drives: N/A
• Target of Infection: Copies itself to the floppy disks as Doc1.doc.exe.
• Time Stamp of Attachment: N/A

TECHNICAL DETAILS

When W32.Wilsef is executed, it does the following:

1. Creates the following files:
   • %Windir%Regsysw.com, (31,232 bytes), detected as W32.Wilsef
   • %Windir%Unistw1.com, (692,339 bytes), detected as W32.Wilsef
   • A:Doc1.doc.exe, (692,339 bytes), another copy of Unistw1.com, detected as W32.Wilsef
   • %System%Regocx.exe, (10,000 bytes), non-viral utility, not detected
   • %System%Msvbvm60.dll, (745,984 bytes), a UPX-packed version of a Visual Basic .dll, not detected.
   • <Same folder as the virus>F#F$_Readme.exe, (31,232 bytes), a temporary copy of Regsysw.com, detected as W32.Wilsef
     
     

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

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2. Adds the value:
   
   "Reg_WFT"="%Windir%Regsysw.com"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the virus runs when you start Windows.
   
   
3. Attempts to contact an FTP server and an HTTP server.
   
   
4. Acts as a backdoor, accepting commands including:
   • Downloading or uploading files
   • Deleting files
   • Executing programs
   • Infecting other files by overwriting them with Unistw1.com

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. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: End the malicious process.
4. Run a full system scan and delete all the files detected as W32.Wilsef.
5. Reverse the changes made to the registry.
6. Optional: Restore Msvbvm60.dll from a backup copy.
   

For 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"

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Note: When you are completely finished with the removal procedure and you are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

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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 ending the malicious process

Windows 95/98/Me
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."

Windows NT/2000/XP
To end the malicious process:
1. Press Ctrl+Alt+Delete once.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to alphabetically sort the processes.
5. Scroll through the list and look for Regsysw.com.
6. If you find the file, click it, and then click End Process.
7. Exit the Task Manager.
   

4. Scanning for and deleting 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.Wilsef, click Delete.

5. Reversing the changes made to the registry

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

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1. Click Start, and then click Run. (The Run dialog box appears.)
   
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the value:
   
   "Reg_WFT"="%Windir%Regsysw.com"
   
   
5. Exit the Registry Editor.

6. Restoring Msvbvm60.dll
W32.Wilsef replaces Msvbvm60.dll with its own version. If you find that some programs are no longer operating as expected, restore the original file from a backup copy or re-install it. Contact Microsoft for information on how to do this.