W2K.Installer.1676

W2K.Installer is a cavity infector and does not change the file size of the infected files. The virus first searches through the code section to find an unused portion that is large enough for the virus to overwrite. These sections are usually filled with 0xCC or 0x90 byte values. When the unused portion is located, the virus overwrites its code into the cavity and places a JMP (0xe9) instruction pointing to the start of the virus body into the entry point code.
The infection happens randomly, but the virus always infects applications with an MSI extension.
MSI is a part of the Windows 2000 Installation Kit. The virus avoids infecting files that are protected by SFC (System File Checker). It marks infected files by modifying the MinorLinkerVersion field of the PE header to 0x29.

The virus contains the following text in the virus code:
[Win2000.Installer] by Benny/29A & Darkman/29A

W2K.Installer does not use any specific Windows 2000 functionality to replicate and it fails to do so under some beta and RC versions of Windows 2000. The virus is unique because of the way it infects files. Similar cavity infection methods were used in older DOS viruses and virus writers are starting to adapt it again in order to avoid being detected by first generation heuristic analyzers.

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