W95.HybrisF

SUMMARY

W95.HybrisF is one of the encrypted plug-ins that are downloaded by the W95.Hybris.gen worm.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) November 17, 2000
• Virus Definitions (Intelligent Updater) November 17, 2000

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: More than 1000
• Number of Sites: More than 10
• Geographical Distribution: Medium
• Threat Containment: Moderate
• Removal: Moderate

Damage

• Damage Level: Low

Distribution

• Distribution Level: High

TECHNICAL DETAILS

This plug-in infects Portable Executable (PE) files (see the Additional Information section below). Only PE files that have a long enough code section 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 SARC detects this plug-in as W95.HybrisF.

Recommendations

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.

REMOVAL

To remove this worm:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Make sure that Norton AntiVirus is set to scan all files.
3. Restart the computer in Safe Mode (Windows 95/98/Me).
   • Windows 95
     1. Exit all programs, and then shut down the computer.
     2. Turn off the computer, and then wait 30 seconds. You must turn off the computer to remove the virus from memory. Do not press the reset button.
     3. Turn on the computer. When you see the "Starting Windows 95" message, press F8.
     4. Type the number for Safe Mode, and then press Enter.
   • Windows 98/Me
     1. Click Start, and click Run.
     2. Type msconfig and then click OK. The System Configuration Utility dialog box appears.
     3. Click the General tab, and click Advanced.
     4. Check Enable Startup Menu, click OK, and then click OK again.
     5. Exit all programs, and then shut down the computer.
     6. Turn off the computer, and then wait 30 seconds. You must turn off the computer to remove the virus from memory. Do not press the reset button.
     7. Turn on the computer, and wait for the menu.
     8. Type the number for Safe Mode, and then press Enter.
        
        NOTE: When you have completed all of the steps in this document, then you may repeat steps 1 through 4. In step 4, uncheck Enable Startup Menu. The next time you restart the computer, you will not see the startup menu.
        
4. Run a full system scan.
   • If Norton AntiVirus detects W95.HybrisF, reboot into Normal Mode and download and run the W95.HybrisF fix tool. This tool will repair any Windows executable files that have been infected by W95.HybrisF.
   • If Norton AntiVirus detects an infection other than W95.HybrisF, choose to repair any infected files. If Norton AntiVirus cannot repair the files, choose to delete them.
5. When the scan has finished, restart the computer into Normal Mode.