You have to use machine filtering of some kind, because there's too much information.

A director of NSA, pre 9/11, once remarked that the entire organization produced about two pieces of actionable intelligence a day, and about one item a week that reached the President. An internal study from that era began "The U.S. Government collects too much information".

But that was from the Cold War era, when the intelligence community was struggling to find out basic things such as how many tank brigades the USSR had. After 9/11, the intel community had to try to figure out what little terrorist units with tens of people were up to. That required trolling through far too much irrelevant information.

A picked nit, perchance, but you may have meant "trawling". Not sure how much trolling the NSA does :)