The US Treasury Department said Monday Chinese state-sponsored hackers broke into its systems earlier this month.
In a letter informing lawmakers of the breach, the department said Chinese hackers remotely accessed Treasury workstations and stole unclassified documents.
The hack is being treated as a "major cybersecurity incident."
What do we know about the breach?
The department did not say how many workstations were accessed or what documents the hackers might have taken.
However, it informed lawmakers that a Chinese state-sponsored group compromised BeyondTrust, a third-party software provider, and accessed the Treasury workstations.
"There is no evidence indicating the threat actor has continued access to Treasury systems or information," the department's spokesperson said.
The department said it was working with the FBI and the Cybersecurity and Infrastructure Security Agency to assess the exact scope of the hack.
Chinese cyberattacks against governments
Several countries, notably the US, have expressed concern over alleged hacking activities linked to the Chinese government in recent years.
Beijing has denied these accusations, saying it opposes and actively combats all forms of cyberattacks.