The Dark Web is a term that refers specifically to a collection of websites that are publicly visible, but hide the IP addresses of the servers that run them. Thus they can be visited by any web user, but it is very difficult to work out who is behind the sites. And you cannot find these sites using search engines.
Almost all sites on the so-called Dark Web hide their identity using the Tor encryption tool. You may know Tor for its end-user-hiding properties. You can use Tor to hide your identity, and spoof your location. When a website is run through Tor it has much the same effect.
Indeed, it multiplies the effect. To visit a site on the Dark Web that is using Tor encryption, the web user needs to be using Tor. Just as the end user’s IP is bounced through several layers of encryption to appear to be at another IP address on the Tor network, so is that of the website. So there are several layers of magnitude more secrecy than the already secret act of using Tor to visit a website on the open internet – for both parties (See also: How to delete your Google location history).
Not all Dark Web sites use Tor. Some use similar services such as I2P – indeed the all new Silk Road Reloaded uses this service. But the principle remains the same. The visitor has to use the same encryption tool as the site and – crucially – know where to find the site, in order to type in the URL and visit.
Infamous examples of Dark Web sites include the Silk Road and its offspring. The Silk Road was (and maybe still is) a website for the buying and selling of recreational drugs. But there are legitimate uses for the Dark Web. People operating within closed, totalitarian societies can use the Dark Web to communicate with the outside world. And given recent revelations about US- and UK government snooping on web use, you may feel it is sensible to take your communication on to the Dark Web.More Info