BIOLOGICAL CHERNOBYL. “The largest biological weapons accident known– the anthrax outbreak in Sverdlovsk (now Yekaterinburg) in the Soviet Union in 1979, sheep became ill with anthrax as far as 200 kilometers from the release point of the organism from a military facility in the southeastern portion of the city (known as Compound 19 and still off limits to visitors today) …” All records were expunged.
http://en.wikipedia.org/wiki/Biodefense