Protecting the US from eavesdropping and SIGINT spying by foreign governments and agencies, called "penetration and network warfare."[1][2] The agency does so by clandestine (secret) means,[3] such as bugging electronic systems,[4] and sabotaging their computer networks with viral software.[5][6]
Church Committee, Intelligence Activities and the Rights of Americans: 1976 US Senate Report on Illegal Wiretaps and Domestic Spying by the FBI, CIA and NSA, Red and Black Publishers (May 1, 2008).
Aid, Matthew, The Secret Sentry: The Untold History of the National Security Agency, 432 pages, ISBN978-1-59691-515-2, Bloomsbury Press (June 9, 2009).