The United States Treasury Department has added several cryptocurrency addresses allegedly connected to controversial mixer Tornado Cash to the Specially Designated Nationals list of the Office of Foreign Asset Control, or OFAC.

In a Monday announcement, the OFAC effectively barred U.S. residents from using more than 40 USD Coin (USDC) and Ether (ETH) addresses connected to Tornado Cash by placing them on its list of Specially Designated Nationals. It’s unclear what led to this enforcement action, but the protocol was at the center of some recent hacks and exploits in decentralized finance, including a $375-million attack on Wormhole in February and a $100-million hack on Horizon Bridge in June.

Related: US Treasury Dept sanctions 3 Ethereum addresses allegedly linked to North Korea

Tornado Cash announced in July that it had fully open-sourced its user interface code as part of its goals towards complete decentralization and transparency.

This story is developing and will be updated.