W95.Hybris.Plugin

After infecting a system, the W95.Hybris.gen worm attempts to connect to the newsgroup alt.comp.virus. If the worm connects successfully, it does the following:

1. Uploads its own encrypted plug-ins to this newsgroup.
2. Goes through the subject headers of the newsgroup messages, looks for other attached plug-ins, and tries to match a specific format. The subject header will specify the version number of the attached plug-in.
3. If a newer version of a plug-in is found, the worm downloads the more recent module and updates it's behavior.

NOTE: There are numerous plug-ins available, and they have different characteristics. The most common one displays a large spiral that covers the Windows desktop and prevents you from using Windows. Another plug-in has similar behavior, but displays a solid black circle.

The plug-ins may do one or more of the following:

• Generates a spiral image. Depending on system date and time (September 16 and 24, and on 59 minutes of each hour starting in 2001), the spiral image file is run. Upon execution, this plug-in initially loads OpenGL libraries that are used to display a large black and white spiral image. It also registers itself as a service, which prevents the process from being displayed in the Close Program dialog box.
• Infects DOS executable programs. The DOS .exe infection is a fairly simple dropping technique. The virus code is appended to the end of the file with a small 16-bit dropper routine. This routine creates a temporary file with an .exe extension in the \Temp folder, and then executes it. After that, the routine deletes the temporary executable. This infects the Wsock32.dll file with the worm.
• Infects PE executable programs. The PE executable has a much more complicated file infection routine. Only large PE files that have a code section long enough will be infected. The virus infection plug-in packs the original code area and overwrites it, if it will fit in the same place. This complicated antiheuristic infection technique is difficult (but not impossible) to repair. Currently Security Response detects this plug-in as W95.HybrisF. A removal tool has been created to remove this plug-in. Click here to obtain the W95.HybrisF fix tool.
• Infects all .zip and .rar archives on all available drives from C: to Z:. While infecting the .zip and .rar files, the worm renames .exe files in the archive to .ex$ extensions, and adds its copy of the worm to the archive with a .exe extension (this is the companion method of infection).
• Sends messages with encoded plug-ins to the alt.comp.virus newsgroup, and then gets new plug-ins from there.
• Spreads the worm to remote computers that are infected with the Backdoor.SubSeven Trojan. The plug-in detects such computers on the Web, and by using SubSeven commands, uploads a copy of the worm to the SubSeven infected computer.
• Encrypts worm copies with polymorphic encryption loop before sending the copy to others as an email attachment.

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