National Security officials head to Capitol Hill Tuesday to defend data surveillance programs that they say have prevented more than 50 attacks in the United States. General Keith Alexander, is the director of the U.S. National Security Agency. (SOUNDBITE) (English) GENERAL KEITH ALEXANDER, THE DIRECTOR OF THE U.S. NATIONAL SECURITY AGENCY, SAYING: "In recent years these programs, together with other intelligence, have protected the U.S. and our allies from terrorist threats across the globe to include helping prevent the terrorist--, the potential terrorist events over 50 times since 9/11." Sean Joyce the Deputy Director of the FBI offered details. (SOUNDBITE) (English) SEAN JOYCE, THE DEPUTY DIRECTOR OF THE FEDERAL BUREAU OF INVESTIGATION, SAYING: "In the fall of 2009, NSA using 702 authority intercepted an e-mail from a terrorist located in Pakistan. That individual was talking with an individual located inside the United States, talking about perfecting a recipe for explosives. Through legal process, that individual was identified as Najibullah Zazi. He was located in Denver, Colorado. The FBI followed him to New York City. Later we executed search warrants with the New York Joint Terrorism Task Force and NYPD and found bomb-making components in backpacks." They also said surveillance programs were instrumental in identifying Pakistani-American David Headley as a co-conspirator in the Mumbai bombings that killed166 people in India in 2008.