W32.ElKern.3326

Removal using the removal tool:
Symantec has provided a tool to remove infections of all known variants of W32.Klez and W32.ElKern.

Note on W32.Klez.gen@mm detections: W32.Klez.gen@mm is a generic detection for variants of W32.Klez. Computers that are infected with W32.Klez.gen@mm most likely have been exposed to either W32.Klez.E@mm or W32.Klez.H@mm. If your computer is detected as infected with W32.Klez.gen@mm, download and run the tool. In most case, the tool will be able to remove the infection.

Manual removal
When this virus infects files, it can behave as either a cavity infector or an appender. This means that the virus can inject itself into the host file in such a fashion as to not increase the file's overall size.

Once the virus is activated, it creates a new thread for its own execution and then gives control directly to the original host program.

The virus creates a copy of itself in the \Windows\System folder. Norton AntiVirus detects this file as W32.ElKern.3326 (dr). The file name differs, depending on the Windows version:

• Windows 95/98/Me: %System%\Wqk.exe
• Windows NT/2000: %System%\Wqk.dll

NOTE: %System% is a variable. The worm locates the \Windows\System folder (by default this is C:\Windows\System or C:\Winnt\System32), and copies itself to that location.

It then does the following, depending on the Windows version:

• Windows 95/98/Me
  It adds the value
  
  WQK   %System%\Wqk.exe
  
  to the registry key
  
  HKEY_LOCAL_MACHINE\Software\Microsoft\
  Windows\CurrentVersion\Run
  
  This causes the virus to run each time that you start Windows.
  
• Windows NT/2000
  It adds the value
  
  AppInit_DLLs  %System%\Wqk.dll
  
  to the registry key
  
  HKEY_LOCAL_MACHINE\Software\Microsoft\
  Windows NT\CurrentVersion\Windows
  

The virus then attempts to infect all executable files in the %System% folder (and its subfolders). It sleeps for a random period of time between each file that it tries to infect.

NOTE: When the virus searches for files to infect, this virus ignores the file extensions. The virus checks each file to see if it is a valid Windows executable before infecting it. However, it does not infect .dll files.

During the infection process this virus infects all drives on the computer (including mapped ones). This virus also searches through all available network resources for open shares, which it then tries to infect.

Due to a bug, the virus will crash a computer running Windows 9x if any of these shares are write-protected.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• 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.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. 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.
• If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.

Summary