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A website used by criminals to buy and sell credit card details and bank log-ins has been shut down after a police operation, the BBC has learned.
International forum Darkmarket ran for three years and led to fraud totalling millions of pounds.
Nearly 60 people connected with the site have been arrested in cities including London and Manchester as well as in Germany, Turkey and the US.
The FBI spent two years gathering evidence after infiltrating the site.
The Serious Organised Crime Agency (Soca), which has been leading the UK investigation, said it was "a one-stop shop" for criminals.
The arrests were made after computer experts, including some former hackers, followed electronic trails left by site users.
A total of 11 people were arrested in the UK. As well as London and Manchester, raids took place in Leicester, Humberside and South Yorkshire.
Darkmarket was strictly invitation-only and gave criminals access to a wide range of valuable personal information.
The data held on the magnetic strip of an ordinary credit card was available to buy for as little as one pound.
Most prized were corporate credit cards belonging to frequent business travellers.
Soca deputy director Sharon Lemon said these were highly sought after because they could be used by criminals all over the world to spend large sums without arousing suspicion.
"Darkmarket is a one-stop shop for the online criminal," she said.
"You can go to the forum and engage in criminal activity quite freely. You can buy any product you want, you can sell any product you want."
She stressed that online fraud of this kind was not a "victimless crime" and involved criminals of all levels of sophistication.
"They are taking someone else's money," she said.
"These aren't geeks we're talking about. These are serious and organised criminals.
"And they can vary. You can be the beginner who can go onto the site, get a tutorial and start your life of crime.
"Or you can get people who are fed up. [They think] Actually, Class A drugs are a bit hands-on, why do that when I can make hundreds of thousands online?"
She said there were 2,000 users registered on Darkmarket, but many of those were not unique because one individual could go by a number of online aliases.
Underground forums, such as this one, where hi-tech criminals buy and sell valuable data such as credit card numbers and bank logins can be hard places to find and infiltrate.
While many can be found just be searching on the internet, the publicly-accessible ones tend to be full of conmen looking for victims or people to carry out crimes on their behalf.
BBC News website technology reporter Mark Ward said: "The most serious underground markets operate on an invitation-only basis.
"Getting invited involves building up and maintaining a reputation as an honest criminal on other public places."
He said the information the police and FBI would gather as a result of the raid on Darkmarket would probably lead them to many more underground forums.
The FBI infiltrated Darkmarket in a similar way to a previous sting, known as Operation Firewall, that was carried out against a group known as the ShadowCrew.
It was able to access the group when an administrator who looked after the ShadowCrew's forums was arrested on an unrelated crime.
Following a series of raids, the FBI initially arrested 28 members of the group. Further investigation led to more arrests around the world, including some in the UK.
Mrs Lemon told the BBC that one individual had spent £250,000 on personal data in just six weeks.
"Had he realised the full potential of the information he had, he could have obtained up to £10m," she said.