From seven years ago, Bruce Schneier explains why collecting massive amounts of data won’t allow us to find terrorist patterns hidden within:
Many believe that data mining is the crystal ball that will enable us to uncover future terrorist plots. But we’re not going to find terrorist plots through systems like this. We’re not trading privacy for security; we’re giving up privacy and getting no security in return.
Data mining works best when there’s a well-defined profile you’re searching for, a reasonable number of attacks per year, and a low cost of false alarms. Credit card fraud is one of data mining’s success stories: all credit card companies data mine their transaction databases, looking for spending patterns that indicate a stolen card. Many credit card thieves share a pattern — purchase expensive luxury goods, purchase things that can be easily fenced, etc. — and data mining systems can minimize the losses in many cases by shutting down the card.