U.S. authorities said on Wednesday they have arrested the majority shareholder and cofounder of Hong Kong-registered virtual currency exchange Bitzlato Ltd for allegedly processing hundreds of million of dollars in illicit funds.

Anatoly Legkodymov, a Russian national living in China, was arrested in Miami on Tuesday on charges that he operated the exchange as a “high-tech financial hub that, in his own words, catered to ‘known crooks'”, a top Justice Department official said.

The action, done in conjunction with the U.S. Treasury Department’s Financial Crimes Enforcement Network and foreign authorities, marked the first major action by the Justice Department’s National Cryptocurrency Enforcement Network.

Treasury’s Financial Crimes Enforcement Network (FinCEN) said it has prohibited certain transmittals of funds involving Bitzlato by any covered financial institution after labeling Bitzlato Ltd a “money laundering concern” related to Russian illicit finance.

Reuters was unable to immediately locate contact information for Bitzlato. The firm has processed $4.58 billion worth of cryptocurrency transactions since May 3, 2018, prosecutors said.

By midday Wednesday, Bitzlato’s website was replaced by a notice saying that the service had been seized by French authorities “as part of a coordinated international law enforcement action.”