National Security Agency (NSA), an independent agency within the U.S. Dept. of Defense. Founded by presidential order in 1952, its primary function is to encode and decode communications intelligence and to protect U.S. signals and information systems. The mission of its Information Systems Security department (INFOSEC) is to protect classified and sensitive information stored on government computers or networks. The NSA includes the Central Security Service, established in 1972 to promote a full partnership between the NSA and the cryptological elements of the armed forces, and the National Cryptologic School. The agency, which is headquartered in Fort Meade, Md., is the largest employer of mathematicians in the country. Its director must be a military officer. For many years the NSA was the most hidden of U.S. intelligence agencies; its large budget was secret and its existence barely acknowledged. In December,2005 the knowledge of President George W Bush using the NSA for unlawful domestic spying was released to the press, causing The President to publicly admit to his directives under the pretense of his "War On Terror".