CIH, also known as Chernobyl or Spacefiller, is a Microsoft Windows 9x computer virus that first emerged in 1998. Its payload is highly destructive to vulnerable systems, overwriting critical information on infected system drives and, in some cases, destroying the system BIOS. The virus was created by Chen Ing-hau (陳盈豪, pinyin: Chén Yíngháo), a student at Tatung University in Taiwan. It was believed to have infected sixty million computers internationally, resulting in an estimated NT$1 billion (ca. US$40,000,000) in commercial damages.
Chen claimed to have written the virus as a challenge against bold claims of antiviral efficiency by antivirus software developers.