Trojan.Nullpos

SUMMARY

Trojan.Nullpos is a Trojan horse program that modifies the screen saver settings to display a message written in Japanese. It also moves all the desktop icons to the "My Document" folder. The Trojan spreads using the Winny file-sharing network.

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 18, 2004
• Virus Definitions (Intelligent Updater) August 12, 2004

Threat Assessment

Wild

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

Damage

• Damage Level: Low
• Modifies Files: Moves all short-cut icons from the desktop to the My Documents folder.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Trojan.Nullpos is executed, it performs the following actions:

1. Displays the message:
   
   
   
   
   
2. Copies the file, %System%TASKMGR.EXE, to the %Windows% folder.
   
   
3. Modifies the file, %System%TASKMGR.EXE.
   
   Note: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   
   
4. Moves all the shortcut icons on the desktop to the My Documents<Japanese character string> folder.
   
   
5. Copies itself as %Windows%ugfix<Username>.wab.
   
   
6. Copies itself as %Windows%ugfix<Japanese character string>.zip.
   
   
7. Creates the file, %Windows%ss.reg.
   
   
8. Adds the values:
   
   "ScreenSaveActive"="1"
   "ScreenSaveTimeOut=60"
   "SCRNSAVE.EXE"="%system%ssmarque.scr"
   
   to the registry key:
   
   HKEY_CURRENT_USERControl PanelDesktop
   
   
9. Sets the values:
   
   BackgroundColor=0 0
   Speed=3
   Text=<Japanese character string>
   TextColor=255 0 0
   Size=48
   
   in the registry key:
   
   HKEY_CURRENT_USERControl PanelScreen Saver.Marquee
   
   This enables the following screen saver:
   
   
   
   
   

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. Run a full system scan and repair all the files detected as Trojan.Nullpos.
4. Reset the screen saver.
5. Copy the file %Windows%TASKMGR.EXE to the %System% folder.

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

1. To disable 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"

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


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. To update 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. To scan for and repair the infected files

1. Start your Symantec antivirus software 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 Trojan.Nullpos, click Repair.
   
   Note: If your Symantec antivirus product reports that it cannot repair an infected file, Windows may be using the file. To fix this, run the scan in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode." Once you have restarted in Safe mode, run the scan again.
   
   When all the infected files have been repaired, restart the computer in Normal mode.
   

4. To reset the screen saver

1. Right-click on Windows desktop > Properties.
2. Click the Screen Saver tab and select the desired screen saver.
3. Click Apply > OK.
   

5. To copy the file %Windows%TASKMGR.EXE to the %System% folder
Using Windows Explorer, locate the file Taskmgr.exe in the %Windir% folder and copy it to the %System% folder.