Officials in the US and Europe say they have taken down two of the largest 'criminal marketplaces' on the so-called dark web.
The dark web refers to specific parts of the internet intentionally 'hidden' from search engines, and require specific tools or networks - such as anonymity software such as Tor - to access.
Officials say AlphaBay - which was created in 2014 - was considered the largest of the dark web criminal marketplaces, with hundreds of thousands listings for items such as illegal drugs, toxic chemicals, malware, firearms, and fraudulent IDs.
Hansa, meanwhile, was the third largest marketplace, with European agencies saying it hosted trading of "similarly high volumes in illicit drugs and other commodities".
Dutch National Police - aided by Europol and other European agencies - are said to have taken control of Hansa on June 20th, and monitored activities until it was shut down today.
The FBI and DEA, meanwhile, say they identified a Canadian citizen who is alleged to have been the creator and administrator of AlphaBay.
The suspect - Alexandre Cazes (25) - was arrested in Thailand earlier this month, and is reported to have died in custody the same day AlphaBay 'went dark'.
US police say servers and millions of dollars worth of cryptocurrencies have been seized in connection with their investigation.
According to the US agencies involved in the operations, AlphaBay vendors sold drugs such as fentanyl and heroin, and said "there have been multiple overdose deaths across the country attributed to purchases on the site".
US Attorney General Jeff Sessions described the takedown of AlphaBay as "one of the most important criminal investigations of the year".
He said: "The dark net is not a place to hide. The Department will continue to find, arrest, prosecute, convict, and incarcerate criminals, drug traffickers and their enablers wherever they are.
"We will use every tool we have to stop criminals from exploiting vulnerable people and sending so many Americans to an early grave."
Rob Wainwright, executive director of Europol, added: "The capability of drug traffickers and other serious criminals around the world has taken a serious hit today after a highly sophisticated joint action in multiple countries.
"By acting together on a global basis the law enforcement community has sent a clear message that we have the means to identify criminality and strike back, even in areas of the Dark Web. There are more of these operations to come."
