Chinese government hackers may have broken into the United States Postal Service computer network earlier this year, potentially accessing the information of more than 800,000 government employees and some customers. The hack was initially spotted in September, but wasn’t revealed to the public until today when The Washington Post broke the story.

USPS officials wouldn’t comment on who was behind this cyber attack, though spokesman David Partenheimer told the Post it was “a sophisticated actor that appears not to be interested in identity theft or credit card fraud.” The FBI is reportedly in charge of the ongoing investigation.

Any USPS customers who contacted the agency’s customer care center by phone or email between January 1 and August 16 may be at risk. Hackers were reportedly able to obtain names, email addresses and phone numbers, though the USPS notes that no customer credit card or social security numbers were exposed.

The hackers targeted the Office of Personnel Management as well USIS, an independent contractor focused on security clearance. They managed to get the name, date of birth, social security number, phone number, address, and date of employment for every USPS employee. Still, officials say there’s no reason to worry.

“Fortunately, we have seen no evidence of malicious use of the compromised data,” said Postmaster General Patrick Donahoe. “We are taking steps to help our employees protect against any potential misuse of their data.”