Here’s how phone metadata can reveal your secrets

The National Security Agency’s surveillance program, now being challenged by the American Civil Liberties Union, only collects metadata about Americans’ phone calls—who they call, when, and how long the calls last. In defending the program, the government has cited a controversial 1979 Supreme Court decision that held that phone records are not protected by the Fourth Amendment because consumers do not have a reasonable expectation of privacy in their calling records. But Ed Felten, a professor of computer science at Princeton University (and, Lee’s former graduate school advisor) argues that this understanding of the ruling is wrong. In a legal brief supporting the ACLU’s request, Felten argues that the distinction between call “contents” and “metadata” isn’t always clear. Sometimes, the mere fact that someone called a particular number reveals extremely sensitive personal information, such as when someone calls a suicide or a tax fraud hotline.