What is the dark web?

The internet is often described in layers: the surface web you can search, the much larger deep web of private pages such as email and bank accounts, and the dark web, which is deliberately hidden. Most dark web sites use Tor, based on onion routing developed at the US Naval Research Laboratory in the mid-1990s, which bounces traffic through several encrypted relays. The dark web became notorious through Silk Road, an illegal marketplace launched in 2011 and shut down by the FBI in 2013. Yet it also has legitimate uses for journalists, whistleblowers and people living under censorship. Major outlets including The New York Times and the BBC run official versions of their websites on Tor.