Air Force Personnel Center officials alerted Air Force and federal investigators of unusally high activity on a single user's account, prompting the breach notifications.
Maj. Gen. Tony Przybyslawski, AFPC commander, said in a statement that airmen were notified as quickly as possible.
"We notified the individuals involved outlining what happened and how they can best insulate themselves from this potential risk," he said. "We've taken steps to increase our system security. We're working with the Air Force agencies to identify vulnerabilities. We must keep our data protected."