To guarantee anonymity, Tor had to have mass appeal and so the software was designed to be “open-source”, meaning that the source code could be ­distributed and developed by anybody. “It had to be picked up by the public and used. This was fundamental,” says Sylverson. “If we created an anonymous network that was only being used by the Navy, then it would be obvious that anything popping out or going in was going to and from the Navy.”