The outrage this time seems to stem from the fact that the government is widely collecting call records, not merely those associated with a particular suspect or group. But this fear misunderstands how the program works. From what we know, the NSA runs algorithms over the call log database, searching for suspicious patterns over time.

The effectiveness of data-mining is inversely proportional to the size of the sample, so the NSA must sweep broadly to learn what is normal and refine the deviations. A nongovernment analogue might be the credit card flags that freeze payment when, say, a New Yorker goes on a shopping spree in Phoenix. The Washington Post also revealed Thursday that NSA has a parallel metadata program for Internet address packets called Blarney.

If the NSA’s version of a computer science department operates like the rest of FISA, the government is cautious to ensure that its searches are narrowly tailored and specific protocols are reviewed by FISA judges. Mike Rogers, the Chairman of the House Intelligence Committee, said Thursday that the program had helped disrupt a major domestic terror attack in recent years.