W97M.Killboot

SUMMARY

W97M.Killboot is a macro virus that infects the currently active document and the Microsoft Word Normal.dot template when an infected document is closed. So, once the Normal.dot is infected, clean documents will be infected when they are closed.

W97M.Killboot creates the file C:Setver.exe, which the Symantec antivirus products detect as Trojan.Killboot. If Trojan.Killboot is run, it writes the viral code into the Master Boot Record (MBR); this code can overwrite the MBR on all the physical hard drives with zeroes. Symantec antivirus products detect the viral code in the MBR as Killboot.145 (b).

Protection

• Virus Definitions (LiveUpdate™ Weekly) December 31, 2002
• Virus Definitions (Intelligent Updater) December 31, 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: High

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When W97M.Killboot runs, it performs the following actions:

1. Creates these files:

• C:Setver.exe (1,085 bytes). This file is detected as Trojan.Killboot.
• C:Autoexec.bat (112 bytes). The Autoexec.bat file contains instructions to run C:Setver.exe. This file is also detected as Trojan.Killboot.
  
  
  When the file Setver.exe runs, it checks whether the MBR is already infected. If it is not infected, it writes Killboot.145 (b) into the MBR. The code contained in the compromised MBR will check whether the current system date is greater than the one defined in the viral code. If it is greater, Killboot.145 (b) activates its payload. The payload will erase (fill with zeroes) all the sectors that store the MBR data on all the physical hard drives.
  
  The date stored in the Killboot.145 (b) is defined at the moment when W97M.Killboot drops C:Setver.exe. The macro virus patches C:Setver.exe, so that the payload activation date of the dropped boot virus will be based on the macro virus infection date. However, the macro virus does not take regional settings into consideration when doing so. This may lead to a random date defined in Killboot.145 (b). In this case, the payload activation is based on a random factor.
  

2. In addition, the macro virus compromises the following security settings in Microsoft Word:

• The menu option responsible for the security level is disabled.
• When you open a file that is not a Word document or template, the Convert File dialog box no longer appears.
• When you open a document that contains a macro, the warning message no longer appears by default.

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

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.
2. Run a full system scan and repair all the files detected as W97M.Killboot, delete all the files detected as Trojan.Killboot, and repair the MBR if Killboot.145(b) is detected.

For further details, read the following instructions.

Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate) line at the top of this writeup.
• Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater) line at the top of this writeup.
  
  The 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.

Scanning for and repairing the infected files

1. Start your Symantec antivirus software and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec corporate antivirus product is set to scan All Files."
2. Run a full system scan.
   • If any files are detected as infected with W97M.Killboot, click Repair.
   • If any files are detected as infected with Trojan.Killboot, click Delete.
   • If the MBR is detected as infected with Killboot.145(b), click Repair.