W97M.Evo

The worm is triggered when an infected Microsoft Word document is opened or closed. When the worm is triggered, it does the following:

1. Disables Microsoft Word's macro virus protection.
   
   
2. Disables several Microsoft Word toolbars so that the macro modules cannot be seen.
   
   
3. Creates the file, C:\Evo.txt, which contains a copy of the virus code.
   
   
4. Modifies Autoexec.bat. (This only affects Windows 95/98/Me computers.) As a result, the next time that you start the computer, many files (including .exe and .dll files) will be overwritten with the virus code. This will leave the overwritten .exe and .dll files corrupted and no longer executable.
   
   The code appended to the Autoexec.bat will also attempt to format drives D and E.
   
   The files that will be overwritten are located in the following folders:
   • C:\Windows
   • C:\Windows\System32
   • C:\Program Files\Norton Internet Security Professional
   • C:\Program Files\Norton AntiVirus
   • C:\Program Files\Norton AntiVirus\Quarantine\Incoming
   • C:\Program Files\Microsoft Office\Office10
     
     
5. Attempts to spread to other computers using mIRC, by replacing the file C:\Program Files\mIRC\script.ini.

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