W97M.Cruson.A@mm

SUMMARY

This is a Microsoft Word macro virus that contains code to email itself using Microsoft Outlook.

Protection

• Virus Definitions (Intelligent Updater) August 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: Low
• Payload Trigger: Opening of infected documents
• Payload: Mass emailer
• Large Scale E-mailing: Yes
• Modifies Files: Yes

Distribution

• Distribution Level: Medium
• Subject of Email: From (Word Username)
• Target of Infection: Word document files and templates

TECHNICAL DETAILS

This virus hooks the Microsoft Word event handler that handles the opening of documents in order to run its code. It will infect the global template, Normal.dot, and any Microsoft Word documents when they are opened. The viral body resides in a VB module named "Melissa."

The virus will check the registry for the existence of a registry key and compare its value. If the value is matched, the emailing code is not run. If the value is not there, the virus uses Microsoft Outlook to compose a message in the following format, attach the active and infected documents to the message, and then send it:

Subject: From (Word Username)
Message: I remembered something last night. It is very, very important document. Look in attachment.

After the emailing code runs, the virus then adds the subkey

Cruson

to the registry key

HKEY_CURRENT_USERSoftwareMicrosoftOffice

and sets it to the value used in the initial comparison check. The value contains expletives.

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. Be sure that NAV is configured to scan all files.
3. If any files are detected as infected by W97M.Cruson.A@mm, click Repair.

NOTE: It is not necessary to remove the registry key that the virus added.