Russian government hackers stole highly sensitive U.S. spying tools after a contractor brought classified material home and put it on a computer that used Kaspersky anti-virus software, a former senior intelligence official briefed on the matter told NBC News.
The contractor, whose name has not been made public, worked for the National Security Agency, which specializes in hacking computers and eavesdropping on communications.
The Wall Street Journal, who first reported the story, said the stolen material included secret details about how the NSA penetrates foreign computer networks, the computer code it uses for such spying and how it defends networks inside the U.S.
The report also said it was unclear whether the contractor had lost his job or is facing prosecution. He is not believed to have wittingly cooperated with a foreign government.