Tor is a special part of the internet that requires software, known as the Tor Browser bundle, to access it.
The name is an acronym for The Onion Router – just as there are many layers to the vegetable, there are many layers of encryption on the network.
It was originally designed by the US Naval Research Laboratory, and continues to receive funding from the US State Department.
It attempts to hide a person’s location and identity by sending data across the internet via a very circuitous route involving several “nodes” – which, in this context, means using volunteers’ PCs and computer servers as connection points.
Tor was originally designed by the US Naval Research Laboratory, and continues to receive funding from the US State Department
Encryption applied at each hop along this route makes it very hard to connect a person to any particular activity.
To the website that ultimately receives the request, it appears as if the data traffic comes from the last computer in the chain – known as an “exit relay” – rather than the person responsible.
As well as allowing users to visit normal website anonymously, it can also be used to host hidden sites, which use the .onion suffix.
Tor’s users include the military, law enforcement officers and journalists – who use it as a way of communicating with whistle-blowers – as well as members of the public who wish to keep their browser activity secret.
The network has also been associated with illegal activity, allowing people to visit sites offering illegal drugs for sale and access to child abuse images, which do not show up in normal search engine results and would not be available to those who did not know where to look.
Silk Road 2.0 and other 400 dark net sites operating on the Tor network have been shut down in a joint operation between Europol’s cybercrime centre and the FBI.
Tor network is a part of the internet unreachable via traditional search engines.
The joint operation between 16 European countries and the US saw 17 arrests.
Tor is home to thousands of illegal marketplaces, trading in drugs, child abuse images as well as sites for extremist groups.
Experts believe the shutdown represents a breakthrough for fighting cybercrime.
Among those arrested was Blake Benthall, who is said to have been behind Silk Road 2.0, a marketplace for the buying and selling of illegal drugs.
Silk Road 2.0 launched in October 2013 after the original Silk Road site was shut down and its alleged owner arrested.
The operation also saw the seizure of Bitcoins worth approximately $1 million.
“Today we have demonstrated that, together, we are able to efficiently remove vital criminal infrastructures that are supporting serious organized crime,” said Troels Oerting, head of Europol’s European cybercrime centre.
Silk Road 2.0 and other 400 dark net sites operating on the Tor network have been shut down in a joint operation between Europol’s cybercrime centre and the FBI
“And we are not <<just>> removing these services from the open internet; this time we have also hit services on the dark net using Tor where, for a long time, criminals have considered themselves beyond reach,” he added.
The raid represented both a technological breakthrough – with police using new techniques to track down the physical location of dark net servers – as well as seeing an unprecedented level of international co-operation among law enforcement agencies.
The so-called deep web – the anonymous part of the internet – is estimated to be anything up to 500 times the size of the surface web.
Within that experts refer to the dark net – the part of the network which Tor operates on. There are approximately three million Tor users but the number of sites may be smaller.
Alan Woodward, a security consultant who advises Europol, said that the shutdown represents a new era in the fight against cybercrime.
“Tor has long been considered beyond the reach of law enforcement. This action proves that it is neither invisible nor untouchable,” he said.
However, Alan Woodward added, it did not mean copycat sites would not spring up, or that the police had thrown light on the dark net.