1. Symantec/
  2. Security Response/
  3. W32.Kriz


Risk Level 2: Low

August 11, 1999
February 13, 2007 11:34:21 AM
Systems Affected:

W32.Kriz is a Windows 95/98 virus. It infects Windows Portable Executable (PE) files. The virus resides in memory and attempts to infect any files that are opened by the user or by programs.

NOTE: If you are using Windows 2000/XP, the virus might replicate, but the payload will not be activated.

The virus also modifies the Kernel32.dll file so that it cannot be repaired. In addition, this virus may corrupt some PE files; if this happens, they must be replaced.

The W32.Kriz virus also contains a payload that is executed on December 25 of any year.

The first time the virus is executed on a computer, it creates an infected copy of Kernel32.dll in the \Windows\System folder. The file is named Krized.tt6. This file should be deleted if found.

The next time Windows is started, this file is copied over the original Kernel32.dll. The virus infects other files when certain Windows API functions are called by a program.

There are variants of this virus. Some of the differences between variants pertain to the payload. The 3863 variant accesses more types of drives when overwriting files. Other differences include the method of infection. The 3740 variant creates a new section named "…" and copies its viral code to that newly created section. The 3863 variant simply appends its code to the end of the last section.

Currently, only the 3863 variant has been found in the wild. There is a 3863.b version of this virus. It is the same as the 3863 variant except that some of the unused text at the end of the virus has been corrupted.

If the system date is December 25, then the virus will attempt to flash the BIOS of the computer. This will prevent the computer from starting and may require a change of hardware. Information stored in the CMOS will be cleared, so the date, time, hard drive and floppy drive settings, peripheral configuration, and so forth will need to be restored. The virus also begins overwriting files on all available drives. This includes mapped network drives, floppy disks, and RAM disks. This payload is very similar to W95.CIH.


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.
Writeup By: Eric Chien
Summary| Technical Details| Removal

Search Threats

Search by name
Example: W32.Beagle.AG@mm
STAR Antimalware Protection Technologies
2016 Internet Security Threat Report, Volume 21
  • Twitter
  • Facebook
  • LinkedIn
  • Google+
  • YouTube