W97M.Trug.A

The W97M.Trug.A macro module is executed when Microsoft Word documents are opened or closed.

When the viral macro module runs, it does the following:

1. Disables several Microsoft Word toolbars.
2. Hooks the shortcut keys so that the macro modules cannot be seen.
3. Disables macro virus protection.
   
   NOTE: The first three actions are an attempt by the virus to hide itself from you.
   
4. Deletes all the macro modules from the Microsoft Word global template file, Normal.dot, except for the ThisDocument module.
5. Delete all the macro modules from all the opened documents, except for the ThisDocument module.
6. Exports its code and saves it in the text file, Trugfile.txt.
7. Checks whether the Normal.dot file is infected. If the file is not, it adds itself to the Normal.dot file by importing its viral code from the exported Trugfile.txt. file. The module it adds is named ThisDocument. Once the Normal.dot file is infected, the virus attempts to infect the active document in the same way.
   
   Once the infection has occurred, the virus deletes the Trugfile.txt file.
   
8. Calls the first payload routine. This payload is simply to create the file, C:\Trugsting.msg.txt, on the 18th of each month. The Trugsting.msg.txt file contains some text from the author of the virus.
9. Calls the second payload routine. The second payload is executed on the 22nd of each month and is very destructive. This payload creates the file, C:\Autoexec.bat, and adds the commands to that particular file that attempts to delete several system files, including Io.sys.
   
   If the operating system is Windows 95/98/Me and this payload is executed, and if you restart the computer, the system files will be deleted and the computer will no longer start.

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