Domestic intelligence programs run by the National Security Agency (NSA) have "disrupted" more than 50 potential terrorist attacks against the United States and its allies, NSA chief Gen. Keith Alexander told Congress on Tuesday.
The plots included a previously undisclosed plan to blow up the New York Stock Exchange, Alexander said.
"We can't lose these [intelligence] tools," the NSA chief told House Intelligence panel members on Tuesday.
The 50 foiled attacks disclosed Monday far exceed the dozen or so attacks that Alexander last week told the Senate Appropriations Committee had been thwarted due to the domestic intelligence programs.
But during Tuesday's hearing, Alexander and officials from the FBI and Office of the Director of National Intelligence provided details of a plot to blow up the Stock Exchange in New York.
Code named "Operation Wi-Fi," NSA and FBI analysts were able to track terror suspects in Yemen and inside the United States who were plotting the attack, FBI Deputy Director Sean Joyce told the House panel.
Tuesday was the first time the counterterrorism program was discussed in public.
Using intelligence gathered under NSA's PRISM program, which monitors Internet traffic via major service providers, FBI investigators were able to lure terror suspects from Yemen to the United States.
Upon arrival in the U.S., the suspects were taken into custody by federal agents, Joyce said Monday.
FBI counterterrorism investigators were also able to track a top terrorist financier in San Diego, who was supporting militant extremist groups in Somalia.
Federal investigators were able to uncover the San Diego-Somalia connection via intelligence gathered from NSA's program to track overseas cellphone calls made on phones running on the Verizon network.
Former NSA contractor Edward Snowden disclosed details of the PRISM program and Verizon program to the media earlier this month.
Counterintelligence officials at NSA are in the midst of a “damage assessment” to see what other top-secret information Snowden leaked about the agency’s intelligence programs.
The PRISM program led to the breakup of al Qaeda operative Najibullah Zazi’s plot to bomb New York’s subways in 2009, Alexander said during a Senate appropriations panel hearing last Wednesday.
The Verizon cellphone program played a key role in the federal manhunt for Tamerlan and Dzhokhar Tsarnaev, the brothers accused of bombing the Boston Marathon in April.