W32.Weird

W32.Weird creates a hidden process that opens an IP port and listens for commands. This hidden process is similar to other client/server Trojan horses such as NetBus, Backdoor, and BackOrifice. Upon execution of an infected file, W32.Weird creates a file with 10 KB of viral code in the \Windows folder. The name of this file is based on the computer name of the infected system. This 10-KB file contains the server application.

NOTE: This virus will locate Windows even if it is installed to a location other that \Windows. If that is the case in your situation, make the appropriate substitution when reviewing the information in this document.

The virus then creates a copy of Explorer.exe in the in the \Windows folder. The new file has the same file name, different one-character extension, for example, Explorer.3. This new file is infected.

Next, W32.Weird creates a Wininit.ini file that contains a command to rename the infected version of Explorer to Explorer.exe. When Windows is restarted, the infected version of Explorer is executed.

Windows 2000
Additional information for users of Windows 2000 only:
The virus does not appear to properly infect Windows 2000 systems. When executed on such a system, it does not create the 10 KB viral file in the \Winnt folder, but it does create the viral copy of Explorer.exe in the \Windows folder. It also creates the Wininit.ini file which is supposed to rename Explorer.exe when Windows is restarted. However, when the system actually restarts, the file does not get renamed as intended, and the Wininit.ini file is still present.

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