Army Gen Keith Alexander said the two recently disclosed programs one that gathers US phone records and another that is designed to track the use of US-based Internet servers by foreigners with possible links to terrorism are critical in the terrorism fight.
Intelligence officials last week disclosed some details on two thwarted attacks one targeting the New York subway system, one to bomb a Danish newspaper office that had published the cartoon depictions of the Prophet Mohammad.
Under questioning, Joyce said the NSA was able to identify an extremist in Yemen who was in touch with an individual in Kansas City, Missouri. They were able to identify co-conspirators and thwart a plot to bomb the New York Stock Exchange.
Joyce also said a terrorist financier inside the US was identified and arrested in October 2007, thanks to a phone record provided by the NSA. The individual was making phone calls to a known designated terrorist group overseas.
More From This Section
The programs "assist the intelligence community to connect the dots," Alexander told the committee in a rare, open congressional hearing. He said the intelligence community would provide the committees with more specific on the 50 cases as well as the exact numbers on foiled plots in Europe.
Alexander got no disagreement from the leaders of the panel, who have been outspoken in backing the programs since Edward Snowden, a 29-year-old former contractor with Booz Allen Hamilton, disclosed information to The Washington Post and the Guardian newspapers.
"It is at times like these where our enemies within become almost as damaging as our enemies on the outside," Rogers said.
Ruppersberger said the "brazen disclosures" put the United States and its allies at risk.
The general counsel for the intelligence community said the NSA cannot target phone conversations between callers inside the US even if one of those callers was someone they were targeted for surveillance when outside the country.