The U.S. Treasury Department has disclosed a cyber breach by a China state-sponsored actor, which it described as a "major incident." In a letter to lawmakers, the department reported that hackers accessed employee workstations and unclassified documents earlier in December. The attackers exploited a compromised API key from a third-party software provider, BeyondTrust, allowing remote access to Treasury systems. The hack is linked to the Chinese hacking group known as "Salt Typhoon," which has also targeted at least nine U.S. telecommunications firms, including AT&T and Verizon. Both companies have confirmed the breaches and stated that their networks are now secure. The attack is part of a broader Chinese cyber espionage campaign affecting U.S. telecommunications networks and government agencies. Beijing has denied the accusations, with a Foreign Ministry spokesperson calling them "groundless."