The NSA has also conducted a regular program to monitor phone conversations. The agency and the FBI, now cooperating much as the original Senate-House report urged them to do, won a secret order from the Foreign Intelligence Surveillance Court on April 25, giving the government unlimited authority for three months to amass the telephone records of millions of U.S. customers of Verizon, according a report in The Guardian. Sen. Dianne Feinstein, D-Calif., the chairwoman of the Senate Intelligence Committee, said the order appeared to be merely a "three-month renewal of what has been in place for the past seven years." Feinstein and many other senators defended the program that they themselves set in motion in the last decade. Rep. Mike Rogers, R-Mich., chair of the House intelligence committee, said that "within the last few years, this program was used to stop a terrorist attack in the United States."

Nonetheless, the NSA/FBI programs have raised very real concerns over whether this domestic surveillance has violated constitutional protections of privacy for Americans, despite efforts to restrict the data collection to foreign sources. Intelligence professionals counter that the perception of a Big-Brother-like surveillance state must be balanced against the equally real concerns about tracking terrorists that date back to 9/11, issues that have still not been fully resolved today.

The challenge is that even now, in spite of these programs, the intelligence community remains overwhelmed by data, and as the Boston Marathon bombings in April showed, it is very difficult to piece together clues in time to stop an attack. "There are massive gaps in our ability to actually analyze data. Much of the data just sits there and nobody looks at it," says one former NSA official who would discuss classified programs only on condition of anonymity. "People can do pretty horrific things on their own. Whether with explosive devices, or chemicals or biological agents. Everybody's walking around with these devastating weapons. How are you going to stop that?"

Intelligence professionals say that it is only with mass data collection that they can find the key "intersections" of data that allow them to piece together the right clues. For example, if an individual orders a passport and supplies an address where some suspicious people are known to be, that might raise some concerns - without, however, leading to a definite clue to a plot. Yet if the same person who ordered the passport also buys a lot of fertilizer at another address, then only the intersection of those two data points will make the clues add up to a threat that authorities can act on. In a Jan. 30, 2006 op-ed in The New York Times headlined "Why We Listen," former NSA senior director Philip Bobbitt provided a vivid example of how this "threat matrix" works. On Sept. 10, 2001, he wrote, the NSA intercepted two messages: ''The match begins tomorrow'' and ''Tomorrow is zero hour.'' They were picked up from random monitoring of pay phones in areas of Afghanistan where Al Qaeda was active. No one in the intel community knew what to make of them, and in any case they were not translated or disseminated until Sept. 12. But, Bobbitt wrote, "had we at the time cross-referenced credit card accounts, frequent-flyer programs and a cellphone number shared by those two men, data mining might easily have picked up on the 17 other men linked to them and flying on the same day at the same time on four flights."