The U.S. Treasury Department on Friday imposed sanctions on alleged hacker Yin Kecheng and cybersecurity company Sichuan Juxinhe Network Technology Co., accusing both of being involved in a series of hacks against American telecom companies.

US Treasury Secretary Janet Yellen’s computer was infiltrated and unclassified files were accessed as part of a broader breach of the agency by Chinese state-sponsored hackers, according to two people familiar with the matter.

A cyberattack on the US Treasury Department by Chinese state-backed hackers compromised computers of senior officials, including Janet Yellen. The breach, stemming from a third-party provider vulnerability,