Is telephone metadata sensitive? The debate has taken on new urgency since last summer’s NSA revelations; all three branches of the federal government are now considering curbs on access.

Consumer privacy concerns are also salient, as the FCC assesses telecom data sharing practices.

President Obama has emphasized that the NSA is “not looking at content.” “[T]his is just metadata,” Senator Feinstein told reporters. In dismissing the ACLU’s legal challenge, Judge Pauley shrugged off possible sensitive inferences as a “parade of horribles.” On the other side, a number of computer scientists have expressed concern over the privacy risks posed by metadata.

Since the first of many leaked documents showed that the NSA has been gathering phone records as part of its anti-terrorism program, there's been an ongoing fight over just what these records reveal.

To supporters, the metadata collection is a limited system that's rarely queried and doesn't contain enough information to be considered an invasive search: the NSA has said it doesn't collect either the content of calls or the names attached to phone numbers.

As many technology and legal experts on the other side say, though, metadata matters, and a Stanford Security Lab project demonstrates that removing names from a database doesn't effectively mean much.