Security researchers have discovered that an unsecured backup drive has compromised thousands of U.S. Air Force documents, including personnel files and sensitive forms filled out by senior and high-ranking officials. These files were openly accessible because they were located on a backup drive connected to the internet wasn’t password protected.

The compromised files include the names, ranks, addresses, and Social Security numbers of over 4,000 Air Force officers. Other files included the security clearances of hundreds of Air Force officers, including top secret clearance.

Another exposed file included completed applications for national security clearances, which include highly sensitive information that could be used by foreign enemies and spies.