Chinese Government hackers are suspected of breaching the computer networks of the United States Postal Service, compromising the data of more than 8,00,000 employees — including the Postmaster General’s.

The intrusion was discovered in mid-September, said officials, who declined to comment on who was thought to be responsible. The FBI is leading the investigation into the hack.

The Chinese Government has consistently denied accusations that it engages in cybertheft and notes that Chinese law prohibits cybercrime. But China has been tied to several recent intrusions, including one into the computer systems of the Office of Personnel Management and another into the systems of a government contractor, USIS, that conducts security-clearance checks.

The intrusion into the USPS, officials said, was carried out by a sophisticated actor who did not appear to be interested in identity theft or credit card fraud.

“It is an unfortunate fact of life these days that every organisation connected to the Internet is a constant target for cyber intrusion activity,” Postmaster General Patrick Donahoe said in a statement. “The United States Postal Service is no different. Fortunately, we have seen no evidence of malicious use of the compromised data and we are taking steps to help our employees protect against any potential misuse of their data.”

The compromised data included names, dates of birth, Social Security numbers, addresses, dates of employment and other information, officials said. The data of every employee were exposed.