W97M.Killboot

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":

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• 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.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. 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.
• If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.

Summary