W2K.Installer.1676 | 
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W2K.Installer virus is the first known virus to replicate only under Windows 2000. Although this virus may be referred as a Windows 2000-specific virus, it does not use any Windows 2000-specific functionality to replicate. It spreads only under Windows 2000 because the virus checks the version of Windows before it propagates.
Damage
- Payload: This threat does not have a payload
Distribution
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.
Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":
- Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
- If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
- 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.
- Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
- Isolate infected computers quickly to prevent further compromising your organization. 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 you believe you have been infected, please download the latest virus definitions via LiveUpdate or from the Symantec Security Response Web site.
- Click here for instructions on using LiveUpdate to retrieve virus definitions.
- Click here to manually download and install virus definitions from the Symantec Security Response Web site.
Write-up by: Peter Szor
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