In the 'deep web', Freenet software allows users complete anonymity as they share viruses, criminal contacts and child pornography.

The modern internet is often thought of as a miracle of openness – its global reach, its outflanking of censors, its seemingly all-seeing search engines. "Many many users think that when they search on Google they're getting all the web pages," says Anand Rajaraman, co-founder of Kosmix, one of a new generation of post-Google search engine companies. But Rajaraman knows different. "I think it's a very small fraction of the deep web which search engines are bringing to the surface. I don't know, to be honest, what fraction. No one has a really good estimate of how big the deep web is. Five hundred times as big as the surface web is the only estimate I know."

"The darkweb"; "the deep web"; beneath "the surface web" – the metaphors alone make the internet feel suddenly more unfathomable and mysterious. Other terms circulate among those in the know: "darknet