Washington, November 11 (RHC)-- The United States Postal Service (USPS) said on Monday the personal information of its employees as well as some of its customers may have been compromised in a cyber attack.

The USPS said the information obtained in the attack may include employees' names, birthdates, Social Security numbers, addresses, emergency contacts, and other data.

The FBI and other federal agencies are investigating the hacking attack. The cyberattack was carried out by a "sophisticated actor," USPS spokesman David Partenheimer said in a statement.

"We began communicating this morning with our employees about this incident, apologized to them for it, and have let them know that we will be providing them with credit monitoring services for one year at no charge to them," Partenheimer said.

Customers at local post offices or those using the USPS website were reportedly not affected. However, people who used the agency's call center may have had telephone numbers, email addresses, and other information hacked.

The U.S. Postal Service employs over 800,000 workers but provided no information on how many people may have been affected.