Officials at the Army National Guard are advising former and current members to check their credit reports after personal data was discovered to have been exposed.
National Guard Bureau spokesman Maj. Earl Brown said a contract employee inadvertently transferred files containing personal information to a non-Department of Defense-accredited data center.
The data includes names, social security numbers and home addresses and the breach could affect current and former members dating back to 2004.
The National Guard said it does not believe the data will be used unlawfully.
"This was not a hacking incident, in which the intent was to use data for financial gain," Brown said.
The Guard also said this is unrelated to the hack at the federal Office of Personnel Management (OPM) in which the records of nearly 22 million people were stolen from OPM servers.
Chinese hackers are the chief suspects, although the Obama administration officially has not blamed China or anyone else.
Beth Cobert, U.S. Chief Performance Officer and Deputy Director for Management at the Office of Management and Budget took her place Saturday.