Wired.com Article on Mark Klein's evidence of a NSA spy hub at AT&T.
As the above article shows, there is a massive effort on behalf of NSA to scoop up large streams of communications intelligence. The problem is then; what do you do with all that information once you have it? The answer is searching algorithms, that pick up on key words or phrases.
The Flagging Algorithm
The Flagging Algorithm is an automated threat level assessment program, which continuously monitors potential threats, and assigns them different threat levels depending how many red flags they recieve.
Michael Ruppert's article on the PROMIS software: http://www.fromthewilderness.com/free/pandora/052401_promis.html