Narcotics trafficking and money laundering were the main business for Hydra, which researchers say was the largest dark-web market.

The work is part of DOJ's plan to target the infrastructure supporting cybercrime.

Prosecutors found access keys to the wallet containing the stolen cryptocurrency in Ilya Dutch Lichtenstein's cloud storage. The judge called the evidence a "smoking gun." 

"A huge amount of cryptocurrency-based money laundering ... goes through services with substantial operations in Russia," Chainalysis reports.

The Justice Department says it's the agency's largest recovery of stolen cryptocurrency to date.

As law enforcement agencies get better at tracing cryptocurrency, such laundering services have grown in importance.