• The U.S. Treasury Department was hacked by Chinese-backed actors in what the agency called a “serious cybersecurity incident.”
• Hackers accessed “certain unclassified documents” through Treasury workstations, a Treasury official wrote.
• The US is also investigating years of hacker attacks from China. Microsoft called the group “Salt Typhoon.”

Chinese-backed hackers have accessed some computers at the U.S. Treasury Department, the agency told Congress in a letter on Monday.

The Treasury Department learned of the hack on Dec. 8 when BeyondTrust, a third-party software provider, informed the agency that a hacker had gained access to a key that BeyondTrust had used to gain access to a cloud-based service, who provided remote technical support.

Aditi Hardikar, the Treasury Department’s deputy administrative secretary, wrote in the agency’s letter that the hackers accessed “certain unclassified documents” through Treasury workstations.

The breach is considered a “serious cybersecurity incident,” Hardikar wrote. According to your letter, the hackers still do not have access to the agency’s information.

The Chinese embassy in Washington DC responded to the accusation, saying in a statement to Bloomberg that the US was carrying out “incitement attacks against China without any factual basis.”

“The US must stop using cybersecurity to denigrate and slander China and stop spreading all kinds of disinformation about the so-called Chinese hacker threat,” the Chinese embassy added.

The embassy did not immediately respond to a request from Business Insider for comment outside of regular business hours.

A BeyondTrust spokesperson told BI that a “limited number of customers” were involved in the security incident. Customers have been notified and offered assistance, he added.

Georgia-based BeyondTrust holds more than $4 million in federal contracts, according to a Bloomberg compilation of government data.

News of the Treasury Department hack comes as the U.S. government continues to investigate what U.S. security officials say is a years-long hacking campaign that originated in China.

The investigation began in the summer after warnings from Microsoft, which called the hacker group Salt Typhoon.

White House deputy national security adviser Anne Neuberger told reporters earlier this month that while millions of Americans’ data was likely compromised, the hack targeted senior U.S. officials.

“We believe that the calls they recorded and received were directed more at senior politicians,” she said.