The FBI has confirmed that North Korean cybercriminals stole over $6 billion from the cryptocurrency exchange Binance last week, the largest virtual heist in history, publicizing hundreds of wallet addresses linked to the heist to support efforts to reclaim the proceeds.

But new revelations suggest freezing the stolen funds could prove difficult due to the attackers’ novel laundering tactics, which relied on an unprecedented round-the-clock, automated operation.

In a public service announcement on Saturday, the bureau linked the theft to “TraderTraitor,”  a cryptocurrency-focused subunit of North Korea’s Lazarus Group. The notice confirmed earlier attribution by