Secret US surveillance has foiled more than 50 terror plots since 2001, including a planned bomb attack on the New York Stock Exchange, a US spy chief said Tuesday, defending leaked programs, AFP reports.
Google, meanwhile, asked a federal surveillance court to grant it permission to release the number of national security requests and secret court orders it has received in order to be more transparent with users.
Since the disclosure of vast government surveillance programs targeting phone logs and Internet data, Silicon Valley firms have scrambled to respond to users angered by perceived privacy violations. The government has defended the programs as fully legal and vital to preventing terror attacks.
National Security Agency Director General Keith Alexander described four thwarted plots, including a plan to bomb the New York subway he called "the first core Al-Qaeda plot since 9/11, directed from Pakistan."
Alexander, FBI Deputy Director Sean Joyce and others defended the digital snooping, which they insisted has kept America safe since 2001, but which has come under global criticism following leaks of classified details.
"In recent years, the information gathered from these programs provided the US government with critical leads to help prevent over 50 potential terrorist events in more than 20 countries around the world," Alexander said, adding that at least 10 threats were "homeland-based."
He told the House Intelligence Committee that most details were classified and would not be made public.
But in an effort to win political support for the spy programs, details of four incidents, including the New York Stock Exchange plot, were released.
Joyce said a tip from the NSA, which had traced international phone calls from terror suspects to Kansas City, led the FBI to get a court order to begin electronic surveillance on Khalid Ouazzani.
FBI agents then determined that Ouazzani had provided information and support for a "nascent" plot to bomb the NYSE, and arrested him and his co-conspirators.
In May 2010, Ouazzani pleaded guilty to conspiring to provide material support to Al-Qaeda, but the FBI made no mention of a plot to bomb the stock exchange at the time.
The controversy over the spying programs erupted after rogue defense contractor Edward Snowden leaked details of them to Britain's Guardian newspaper and The Washington Post earlier this month.
According to material leaked to the Guardian, the NSA acquires the call logs of Americans from phone companies and monitors digital communications with data obtained from Internet titans like Apple, Facebook and Google.
US officials insist the phone metadata includes no names or addresses, that investigators must obtain a separate order to listen in on calls, and that the Internet data searches were only carried out on foreigners residing abroad.
"If you're looking for a needle in the haystack, you have to have the haystack first," Deputy Attorney General James Cole testified, referring to the huge amounts of raw data, which he said were only used "sparingly."
According to Cole, the database was queried 300 times last year, and only after a secret court set up under the Foreign Intelligence Surveillance Act determined there was reasonable suspicion to pursue a suspect.
Critics have slammed the spying operations as government overreach, insisting the public has the right to know the scope of the programs and the role major Internet firms played in surrendering personal data to authorities.
Google and other firms say they have received thousands of requests for information targeting tens of thousands of accounts.
But they are not allowed to provide a tally of national security and secret FISA court requests separate from ordinary criminal warrants and subpoenas.
Google, which has long published data on criminal requests in its "transparency report," said it should be allowed to disclose separate tallies.
"Lumping national security requests together with criminal requests -- as some companies have been permitted to do -- would be a backward step for our users," a Google spokesperson said.
In its court filing, Google said that its "reputation and business has been harmed by the false and misleading reports in the media, and Google's users are concerned by the allegations."
The company said it was asking the court to affirm its "right" under the First Amendment of the US Constitution to publish the information.