X97M.Sufe.D

SUMMARY

X97M.Sufe.D is a macro virus that infects Microsoft Excel worksheets. It replicates by exporting the entire viral module to a file named C:Ms_IO.sys, and then importing it to new worksheets. This macro virus has a payload that can be executed twice each month.

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 14, 2002
• Virus Definitions (Intelligent Updater) August 8, 2002

TECHNICAL DETAILS

When a Microsoft Excel spreadsheet that is infected with X97M.Sufe.D is opened or closed, the macro virus is activated. The virus then does the following:

First, the virus verifies that the Command.dos file exists in the C:Ms_dos folder. If it does not exist, the virus creates both the folder and the file. The Command.dos file contains the viral macro module. The virus replicates by importing itself from a file that it creates (C:Ms_io.sys) to worksheets that are not infected. To speed its actions and make them invisible, the macro virus temporarily turns off screen updating.

X97M.Sufe.D changes the following Excel options:

• Each time that Excel starts, the alternate startup is set to C:Ms_dos, so that an infected Command.dos file runs the viral macro code.
• The default folder for items such as documents, templates, and graphics is set to C:My Documents.
• Excel is modified to prevent the computer from responding with sound when an error occurs.
• The IntelliMouse is set to scroll instead of zoom.

If the day is the 1st or 20th day of the month and it is Saturday or Sunday, X97M.Sufe.D activates its payload. The virus performs the following actions:

• The Excel window is maximized so that it fills the entire screen and hides the application title bar.
• The virus hides the "Full Screen" CommandBar object, the displayed headings, the outline symbols, any zero values that would be displayed, both horizontal and vertical scroll bars, the workbook tabs, and the displayed grid lines.
• It inserts junk data into the new or existing worksheet. The inserted cells are formatted to display the following:
  
  

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

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions, run a full system scan, and repair all files that are detected as X97M.Sufe.D. Delete C:Ms_io.sys and C:Ms_dosCommand.dos if they exist.
2. Restore the Excel options that X97M.Sufe.D changed.

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

To scan for and repair or delete the infected files:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time 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 have undergone full quality assurance testing by Symantec Security Response. They 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.
     
2. 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.
3. Run a full system scan.
4. If any files are detected as infected by X97M.Sufe.D, click Repair.
5. Use Windows Explorer to look for the following files, and delete them if they exist:
   • C:Ms_io.sys
   • C:Ms_dosCommand.dos

To restore the Microsoft Excel options:
This is optional, but recommended.

NOTE: These are basic instructions and are provided for your convenience. For additional information read the Microsoft Excel Help on these subjects, or contact Microsoft Technical Support.

1. Start Microsoft Excel.
2. Click View, and then click Full Screen to restore the application windows.
3. Click Tools, and then click Customize. Restore the toolbars that the virus disabled.