Discovered in the fall of 1999, the Kriz virus (known more formally as W32.Kriz, W32.Kriz.dr, or PE_KRIZ) infects files on Windows 9x and Windows NT and 2000 systems. It has a potentially devastating payload that triggers on December 25th of any year once an infected file is run. When this happen the virus overwrites files on the floppy disc drive, hard drive, RAM drive, and network drives. It also erases the information stored on the computer's basic input/output system ( BIOS ). Although this can only happen on certain types of BIOS systems, a successful attempt could prevent the computer from booting up - even if a floppy disc is used. This behaviour is similar to that caused by the CIH virus . In some cases, the Kriz virus will corrupt the file it infects and cleaning may not be possible.

W32.Kriz is known as a polymorphic virus, meaning it will reside in computer memory until the next time the system is rebooted. This virus encrypts its code, leaving only a small random decryptor. This virus will infect files as they are opened by any application while it is in memory. This will occur when a user scans files as well. In other words, computers users may be infected but not know about the virus until the following Dec. 25.

The Kriz virus is also known as Win32/Kriz, Win32.Kriz.3862, and Win32.Kriz.3740.