Perhaps the most telling comment to come out of the hearings by the House Intelligence Committee regarding the surveillance of phone numbers, first revealed earlier in June, was about haystacks. "In order to find a needle in a haystack," a witness commented, "first you need a haystack."

That haystack refers to the metadata from billions of phone call records provided to the National Security Agency by phone companies in the United States. That haystack is also the term used to describe what is perhaps the biggest of big data initiatives undertaken by the intelligence community to uncover terrorist activity that might threaten the U.S.

Those billions of phone call records provide the data that can be analyzed once a suspect phone number is found outside the country. In one situation that was described by FBI Deputy Director Sean Joyce, the NSA determined that a phone in Yemen had been calling a number in San Diego.

The NSA provided the number to the FBI, which then tracked down the owner of that phone and who else had been called. Eventually the FBI got a court order to tap the phone, and in the process uncovered a plot to attack the New York Stock Exchange, and arrested the people involved.

What's important to understand is that the NSA only keeps the phone metadata, meaning the phone number itself, the number on the other end of the communication and the duration, time and date of the call. All of the other information that's been speculated about, such as GPS coordinates, cell towers used or the contents of the call itself, are not kept by the NSA in some vast database.

Governing all of this are two parts of the Patriot Act. Part 215 governs the collection of phone information, and while there are a lot of things that could be collected, the NSA only collects the phone call metadata. Other agencies may be collecting other information, but the NSA is the ultimate big data user, and as a result that's all it collects.

The NSA collects these as a part of the business records of the phone companies, and it gets court orders from the secret Foreign Intelligence Surveillance Court to obtain the records. The court orders give the NSA approximately the same access that other agencies can get with a grand jury warrant.

The other part of the Patriot Act is Part 702, which allows the collection of e-mail and text messages. The FBI is the agency that collects most of the Part 702 data, but it requires a court order to do so.