The U.S. Postal Service (USPS) reported Nov. 10 that personal data for approximately 800,000 of its employees, including Social Security numbers, dates of birth, addresses, beginning and end dates of employment and emergency contact information, may have been compromised in a cyber-attack.

According to the Postal Service, the cyber-security intrusion is similar to those reported by many other federal government entities and U.S. corporations. USPS also confirmed that more than its employees’ information may have been compromised: data on customers who may have contacted its call center between Jan. 1 and Aug. 16 were also compromised.

Customer credit and debit cards have not been affected, according to the USPS, but breached data may include their names, addresses, telephone numbers; and email addresses.

“The privacy and security of data entrusted to us is of the utmost importance. We have recently implemented additional security measures designed to improve the security of our information systems, including certain actions this past weekend that caused certain systems to be off-line,” David Partenheimer, media relations manager for the Postal Service, said in a statement.

The FBI is leading in the investigation to figure out the source of the breach. The Washington Post reported that the Chinese government may have played a role in the incident.

The Post also reported that officials mentioned that the security breach was carried out by “a sophisticated actor who did not appear to be interested in identity theft or credit card fraud.”

Partenheimer said that employees have already been notified about the incident and USPS will provide those affected with credit monitoring services at no charge for one year.