What is "coreflood"

Coreflood is a trojan horse and botnet created by a group of Russian hackers and released in 2010. The FBI included on its list of infected systems "approximately 17 state or local government agencies, including one police department; three airports; two defense contractors; five banks or financial institutions; approximately 30 colleges or universities; approximately 20 hospital or health care companies; and hundreds of businesses." It is present on more than 2.3 million computers worldwide and as of May 2011 remains a threat.