What is the dark web?
The Dark Web is a tiny area of the Deep Web - a hidden area of the Internet which is not indexed by search engines - used to conduct illegal activity as well as more legitimate purposes such as activism.
In order to visit certain websites, visitors must find the correct .onion address while using the surveillance-busting Tor browser.
There are online marketplaces and forums selling everything from drugs to fake or stolen passports and weaponry, but unfortunately due to the Dark Web's concealed nature, it can also act as a place to find illegal pornography, such as child exploitation.
The Dark Web hit the headlines in August 2015 after it was reported that 10GB of data stolen from Ashley Madison, a site designed to enable bored spouses to cheat on their partners, was dumped on to the Dark Web.
Hackers stole the data and threatened to upload it to the web if the site did not close down, and the threat was acted upon. The spouses of Ashley Madison users began to receive blackmail letters demanding they pay $2500 in Bitcoin or have the infidelity exposed.
In March 2015 the UK government launched a dedicated cybercrime unit to tackle the Dark Web and UK intelligence outfit GCHQ are together creating the Joint Operations Cell (JOC).
In September 2015, security firm Trend Micro, said personally identifiable information (PII), such as addresses, dates of birth and Social Security numbers - all highly useful when committing identity theft - is sold for as little as a dollar online.