Little is known about how U.S. and European law enforcement shut down more than 400 websites, including Silk Road 2.0, which used technology that hides their true IP addresses.

The websites were set up using a special feature of the Tor network, which is designed to mask people’s Internet use using special software that routes encrypted browsing traffic through a network of worldwide servers.

Tor — short for The Onion Router — also allows people to host “hidden” websites with a special “.onion” URL, which are difficult to trace. But law enforcement appears to have figured out a method to find out where sites are hosted, a serious flaw that could pose risks to people who aren’t running websites that sell drugs and weapons.

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