(Reuters) -Chinese language state-sponsored hackers broke into the U.S. Treasury Division earlier this month and stole paperwork from its workstations, in line with a letter to lawmakers that was supplied to Reuters on Monday.

The hackers compromised a third-party cybersecurity service supplier and have been capable of entry unclassified paperwork, the letter mentioned, calling it a “main incident.”

In response to the letter, hackers “gained entry to a key utilized by the seller to safe a cloud-based service used to remotely present technical help for Treasury Departmental Workplaces (DO) finish customers. With entry to the stolen key, the menace actor was in a position override the service’s safety, remotely entry sure Treasury DO consumer workstations, and entry sure unclassified paperwork maintained by these customers.”

After being alerted by cybersecurity supplier BeyondTrust, the Treasury Division mentioned it was working with the U.S. Cybersecurity and Infrastructure Safety Company (CISA) and the FBI to evaluate the hack’s affect.

BeyondTrust, the CISA and the FBI didn’t instantly reply to Reuters requests for remark.