A global child sexual exploitation ring has been taken down by the FBI and Europol, leading to the arrest of hundreds of suspected paedophiles.
Florida man Steven W Chase, 58, was sentenced to 30 years in prison for creating what is believed to have been "the world's largest child pornography website" with more than 150,000 users.
In total some 870 people were arrested or convicted worldwide, including 368 in Europe alone, and so far at least 259 sexually abused children have been identified or rescued from abusers outside the US.
Chase created the website, called 'Playpen', in August 2014 on the Dark Web network Tor, where people can communicate and access material anonymously through "hidden service" websites.
Special Agent Dan Alfin, who had been part of the investigation with the Bureau's Violent Crimes Against Children section, pointed out the initial difficulty in investigating the case.
"Given the nature of how Tor hidden services work, there was not much we could do about it," he said.
However, in December 2014, Chase accidently revealed Playpen's IP address in Florida, prompting a foreign law enforcement agency to contact the FBI.
A copy of the website was seized by US law enforcement; search warrants were issued for email accounts and eventually, said Mr Alfin, "everything led back to Steven Chase".
One month later the FBI, along with support from European and local law enforcement, launched Operation Pacifier to find Playpen's thousands of members.
Europol's executive director Rob Wainwright called it "one of the most important investigations of online child sexual abuse ever conducted".
Using "court-approved network investigative techniques", US law enforcement uncovered IP addresses that helped identify members.
Intelligence packages were compiled and given to law enforcement authorities in a number of countries, including Colombia, Croatia, Czech Republic, France, Ireland, Italy, Slovakia, Spain, Switzerland, and the United Kingdom.
Some criticised the operation for its "unprecedented" use of malware, targeting over 1,000 computers with one warrant.
Steve Wilson, head of Europol's European Cybercrime Centre said: "Those individuals involved in the sexual abuse of children are becoming increasingly forensically aware and are actively using the most advanced forms of anonymisation and encryption to avoid detection.
"Law enforcement needs to be able to use proportionate means to tackle this threat to our children. The internet has no boundaries and does not recognise borders. We need to balance the rights of victims versus the right to privacy."
The investigation was ongoing, and Mr Alfin said: "Members of [Chase's] enterprise who were raping children, who were producing child pornography all around the world-those cases continue to be indicted and prosecuted."
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