Five years ago, Congress killed an experimental Pentagon antiterrorism program meant to vacuum up electronic data about people in the U.S. to search for suspicious patterns. Opponents called it too broad an intrusion on Americans' privacy, even after the Sept. 11 terrorist attacks.

But the data-sifting effort didn't disappear. The National Security Agency, once confined to foreign surveillance, has been building essentially the same system.

(This was previously recommended by Decius here, but I missed it at the time.)