W32.Update.Worm

SUMMARY

W32.Update.Worm is a simple mass-mailing worm that can spread using Microsoft Outlook. The worm is written in a high-level language. However, for the email spreading, the worm creates and executes a VBS script. This worm also can also spread using mIRC.

This worm may also attempt to disable Norton AntiVirus, depending on which version is being used and under which operating system.

NOTE: Virus definitions dated prior to May 28 will detect some components of this worm as Bloodhound.VBS.Worm.

Protection

• Virus Definitions (Intelligent Updater) May 28, 2001

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Medium
• Payload Trigger: Always
• Payload: Attempts to disable NAV

Distribution

• Distribution Level: Low
• Subject of Email: Antivirus Update
• Name of Attachment: AVUpdate.exe
• Size of Attachment: 7 Kb

TECHNICAL DETAILS

When the worm is first executed, it tries to create an entry in the Windows registry. This appears to be used as a check as to whether the worm has already run on the computer.

The worm creates a copy of itself as WindowsAVUpdate.exe. It then tries to send the newly created file to everyone in the Microsoft Outlook Address Book. The worm does this by creating the file Send.vbs directly under the root of drive C and executing it.

The worm drops a Script.ini file. If this Script.ini file is used together with the popular Windows IRC chat client mIRC, it sends AVUpdate.exe to other IRC users as they join the channel that the infected user is in. The worm can "infect" mIRC only if mIRC is installed in any of the following paths.

• C:Mirc
• C:Mirc32
• C:Program FilesMirc
• C:Program FilesMirc32

NOTE: Norton AntiVirus detects the modified Script.ini file as W32.Update.Worm.

Finally, this worm attempts to disable Norton AntiVirus. However, this happens only under Windows 9x and only with some versions of NAV.

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

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is set to scan all files.
3. Delete any files detected as W32.Update.Worm.
4. If the worm was executed on your system, reset all Norton AntiVirus settings back to the original settings, or alternatively, reinstall Norton AntiVirus.