Well not all terrorists take precautions, many are quite stupid and it only takes one to bring a whole network the attention of the NSA. The bigger problem is t

Well not all terrorists take precautions, many are quite stupid and it only takes one to bring a whole network the attention of the NSA. The bigger problem is that even if their false positive rate is really low, they are hoovering so much data that the true positives (dumb terrorists) get drowned out by the noise. http://news.bbc.co.uk/2/hi/uk_news/magazine/8153539.stm http://news.bbc.co.uk/2/hi/uk_news/magazine/8153539.stm It's why this sort of large scale surveillance is really only effective as tool for coercing public dissent ("We know all about you Mr. Michaelwww").