CIH, also known as Chernobyl or Spacefiller, is a Microsoft Windows computer virus. It overwrites critical information on infected system drives, and more importantly, in some cases corrupting the system BIOS. The name "Chernobyl Virus" was coined some time after the virus was already well-known as CIH, and refers to the complete coincidence of the payload trigger date in some variants of the virus and the Chernobyl accident, which happened in the Ukrainian on April 26, 1986.