The US Treasury Department told lawmakers in a letter back in December that its documents and workstations were accessed by an external party in a security breach. It described the attack as "a major cybersecurity incident" and attributed it to a "China state-sponsored Advanced Persistent Threat actor.

Treasury says hackers accessed “certain unclassified documents” in a “major” breach, but experts believe the attack’s impacts could prove to be more significant as new details emerge.

The cyberattack reported earlier this week reached into the Office of Foreign Assets Control and the Office of Financial Research, sections of the agency that oversee economic penalties against other nations and their citizens.