Their findings indicate that an overwhelming majority of their traffic is driven by the Dark Web's darkest activity: the sexual abuse of children.

At the Chaos Computer Congress in Hamburg, Germany today, University of Portsmouth computer science researcher Gareth Owen will present the results of a six-month probe of the web's collection of Tor hidden services, which include the stealthy websites that make up the largest chunk of the Dark Web. The study paints an ugly portrait of that Internet underground: drug forums and contraband markets are the largest single category of sites hidden under Tor's protection, but traffic to them is dwarfed by visits to child abuse sites. More than four out of five Tor hidden services site visits were to online destinations with pedophilia materials, according to Owen's study. That's over five times as many as any of the other categories of content that he and his researchers found in their Dark Web survey, such as gambling, bitcoin-related sites or anonymous whistle-blowing.

The researchers' disturbing statistics could raise doubts among even the staunchest defenders of the Dark Web as a haven for privacy. "Before we did this study, it was certainly my view that the dark net is a good thing," says Owen. "But it's hampering the rights of children and creating a place where pedophiles can act with impunity."