Tens of thousands of paedophiles are using the so-called dark net to trade images of sexual abuse, an investigation by BBC News indicates. Brits are heavily involved in producing and distributing illegal obscene images. Britain's National Crime Agency warned in its 2014 threat assessment that abusers were turning to anonymous sites and encryption technology. The dark net is the term used to refer to parts of the internet that are hidden and can be hard to access without special software. One of the most popular products used to access such areas is called the TorBrowser. It allows people to use Tor, an onion-routing" system which makes a PC's net address untraceable by bouncing the encrypted data it sends through several randomly selected computer servers on a volunteer network - each of which removes a level of encryption - before it reaches its destination. There are also many hidden sites on the network ending in the .onion suffix, which cannot be found using Google or other regular search engines. Tor was first created by the US military but is now also used by pro-democracy campaigners, whistleblowers and journalists operating under repressive regimes. It was used by activists during the Arab Spring to avoid detection. But criminals are also taking advantage of its anonymity. IT experts are divided as to whether it's possible to create a workable "backdoor" into Tor, which would allow users to be identified. But some security specialists believe there are innovative ways to unmask the users of paedophile sites.