The incident was disclosed in a letter sent by the Treasury Department to lawmakers, detailing how the hackers exploited a vulnerability tied to a third-party service provider, BeyondTrust, which was offering remote technical support. Treasury officials classified this breach as a "major cybersecurity incident," indicating that it involved an Advanced Persistent Threat (APT) actor.

According to spokespersons, the Treasury became aware of the intrusions on December 8 and promptly notified law enforcement agencies. Investigations are being led by the FBI, alongside the Cybersecurity and Infrastructure Security Agency and third-party forensic teams, to assess the overall impact of the breach.

Despite the severity of the incident, officials reported no ongoing access to Treasury data following the initial compromise. However, the specifics regarding the types of documents accessed have not been disclosed. The Treasury underscored their commitment to safeguarding data against external threats, while China continues to deny allegations of espionage.

This story is still developing, with further updates expected as investigations progress. For real-time alerts and breaking news, updates are available via the BBC News App and on social media.