X97M.Feng.A.Trojan

SUMMARY

X97M.Feng.A.Trojan is a Trojan horse that resides in Microsoft Excel documents. After X97M.Feng.A.Trojan is activated, it deletes files from various locations on the computer. It then restarts the computer.

Protection

• Virus Definitions (LiveUpdate™ Weekly) December 11, 2002
• Virus Definitions (Intelligent Updater) December 9, 2002

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

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When X97M.Feng.A.Trojan runs, it deletes

• All files that are located in the same folder as the infected workbook
• All files that are located in the C:My Documents folder
• C:io.sys
• C:Config.sys
• C:Msdos.sys
• C:Command.com

X97M.Feng.A.Trojan then saves itself as %Excel Startup%Fuck.xls.

NOTE: %Excel Startup% is a variable that refers to the Microsoft Excel startup folder. Files that are in this folder are automatically executed when you start Excel.

This allows X97M.Feng.A.Trojan to be executed each time that another workbook is opened, during which time it deletes all sheets from the workbook.

Finally X97M.Feng.A.Trojan saves itself as

• C:io.sys
• C:Msdos.sys

It then restarts the computer. As a result of the file deletions and replacements, if the operating system is Windows 95/98/Me, the computer will no longer start.

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

NOTES:

• These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
• If the Trojan has executed on a Windows 95/98/Me-based computer, in most cases you will first have to either restore the deleted files from a clean backup or reinstall the operating system.

1. Update the virus definitions.
2. Run a full system scan, and repair all workbooks that are detected as X97M.Feng.A.Trojan. Files other than infected Excel files should be deleted. Restore deleted files from a clean backup.

For details on how to do this, read the following instructions.

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
• Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
  
  Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

To scan for and repair the infected files:

1. Start your Symantec antivirus software and make sure that it is configured to scan all files.
   • Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec enterprise antivirus products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
2. Run a full system scan.
3. If any workbook files are detected as infected with X97M.Feng.A.Trojan, click Repair. Files other than infected Excel files should be deleted. Restore deleted files from a clean backup.