Four men have been arrested in the UK over links to underground website Silk Road.
Three men in their early 20s have been arrested in Manchester while the fourth, a man in his early 50s has been arrested in Devon - all charged on suspicion of supplying illegal drugs.
The Silk Road website was shut down by the FBI last week following the arrest of Ross Ulbricht, the alleged administrator of the billion dollar operation. The website, which operated on the deep web, allowed people to anonymously buy and sell a range of illegal items including drugs, counterfeit currency, guns and even offered hitmen for hire.
The arrested were made by the newly-formed National Crime Agency (NCA) and follow the arrest of Ulbricht, 29, in San Francisco on Tuesday last. The NCA officers who made the arrests were working closely with law enforcement agencies in the US, and the UK arrests took place just hours after Ulbricht's arrest.
Ulbricht has since appeared in court denying all charges against him which include money-laundering, computer hacking, drug-trafficking and even soliciting a Silk Road user to murder another member of the forum.
Keith Bristow, the NCA's director general, warned users who think they can hide their identity on the internet to think again:
"These arrests send a clear message to criminals; the hidden internet isn't hidden and your anonymous activity isn't anonymous. We know where you are, what you are doing and we will catch you.
"It is impossible for criminals to completely erase their digital footprint. No matter how technology-savvy the offender, they will always make mistakes and this brings law enforcement closer to them."
The Silk Road website was only accessible on the Tor network, a network of websites which are not accessible using traditional web browsers or indexed by search engines such as Google, Yahoo or Bing.
Andy Archibald, head of the NCA's National Cyber Crime Unit, said: "This is only the start of a wider campaign to tackle the 'dark' or 'deep' web and the criminals exploiting it.
"These criminal areas of the internet aren't just selling drugs. It's where fraud takes place, where the trafficking of people and goods is discussed, where child abuse images are exchanged and firearms are traded."
The FBI estimated that during the two-and-a-half-years the Silk Road was in operation it generated revenues of $1.2 billion making up to $80 million in commission for Ulbricht, who was better known on the website as Dread Pirate Roberts.
One million register users
According to the complaint filed by FBI Special Agent Christopher Tarbell at the time the website was shut down there were 13,000 listings for illegal items on the site and almost one million registered users.
As well as using the Tor network to anonymise those using the site, all transactions on the website were conducted using the virtual currency Bitcoins which is untraceable. This has led to problems for the FBI who are currently trying to access the estimated 600,000 Bitcoins held by Ulbricht.