(FOX NEWS) The National Security Agency and Justice Department mounted a vigorous defense of the government’s controversial surveillance efforts on Tuesday, with NSA chief Gen. Keith Alexander claiming they have helped prevent “potential terrorist events” over 50 times since 9/11.

Officials insisted the programs protect Americans from unwarranted intrusion, as they began to shed light on the scope of the secretive effort in a rare public hearing.

Disclosing new details, a top FBI official claimed the surveillance efforts helped disrupt a plot to bomb the New York Stock Exchange. FBI Deputy Director Sean Joyce said NSA officials discovered the scheme while monitoring a known extremist in Yemen, who was in contact with an individual in the U.S. After initiating surveillance, Joyce said, they were able to detect “nascent plotting” to bomb the stock exchange and ultimately disrupt the plot.


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