Comey was asked about criminal use of the so-called dark web — parts of the Internet walled off from ready access — at a House Intelligence Committee hearing on cybersecurity on Thursday. His answer referenced Tor, which was originally known as "the onion router."

Speaking in particular of people who view child pornography, Comey said: "They'll use the onion router to hide their communications. They think that if they go to the dark web … that they can hide from us. They're kidding themselves, because of the effort that's been put in by all of us in the government over the last five years or so, that they are out of our view. "

Comey's statement could be read as an assertion that U.S. law enforcement has found a way to routinely thwart Tor's system for providing anonymity to users. If that's Comey's intended implication, and if it's true, it would would represent an enormous expansion of the U.S. government's known abilities, as well as a significant blow to privacy advocates.