In a hearing Tuesday with the House Permanent Select Committee on Intelligence, the director of the National Security Agency, Keith Alexander, said that since 9/11, there have been more than 50 terror plots thwarted with the help of NSA surveillance programs.
Four of those incidents were detailed at the hearing, including thwarted plots to bomb the New York subway system and the New York Stock Exchange by linking known suspects in Pakistan and Yemen to contacts in the United States.
NSA officials are set to disclose information about the other cases in a private session with lawmakers on Wednesday.
Note that while the Senate Intelligence Committee gets information on 50 plots allegedly thwarted by NSA surveillance, only 4 are identified publicly. And of course the Intelligence Committee members can't reveal the 46 classified claims without being accused of disclosing classified information. So it's still "trust us" on the other 46.