The FBI is investigating a data breach at the U.S. Postal Service in which employees’ personal data may have been compromised. Every person on staff with the Postal Service, from the Postmaster General down to letter carriers, was exposed according to a report from the Washington Post.

Sources familiar with the matter told the publication that the names, dates of birth, Social Security numbers, addresses, dates of employment and other information on more than 800,000 employees was exposed. What’s more, customers that contacted the postal service customer care center via telephone between January 1, 2014, and August 16, 2014, are also at risk.

Customer credit card information, however, was not at risk.

In a statement on the matter, Postmaster General Patrick Donahoe said it is an unfortunate fact of life these days that every organization connected to the Internet is a constant target for cyber intrusion activity.

Donahoe added that they haven’t seen any evidence of malicious use of the compromised data. What’s more, they are taking steps to help employees protect against any potential misuse of their data.

Given the nature of the attack, sources familiar with the matter said Chinese government hackers are the prime suspects in the investigation. Officials overseeing the matter declined to comment on who might be responsible for the security breach which was first discovered in mid-September.