Pierluigi Paganini September 29, 2026

Pentagon personnel agency breach exposed data of 3 million people after attackers accessed a file-sharing server for about nine months.

The U.S. Defense Manpower Data Center (DMDC), which maintains personnel records for the Department of Defense, is notifying people that their personal information was exposed in a data breach. According to the agency, unauthorized users accessed one of its file-sharing servers for roughly nine months.

The breach affects 2.76 million living people and 294,000 deceased individuals, according to a Department of War official. DMDC held at least 60 million records in fiscal year 2024, covering military and civilian personnel, contractors, family members, retirees and veterans.

“The Pentagon has confirmed that the breach affects 2.76 million “living individuals,” a category that potentially includes current and former defense personnel or their dependents, and 294,000 “deceased individuals,” a Defense Department official told CNN on Monday, three days after this story was published.” CNN states.

The Defense Manpower Data Center (DMDC) has notified individuals that a security vulnerability exposed personal information stored on one of its file-sharing systems.

The vulnerability was discovered on July 16, 2026, and the US office quickly patched the system and restored it. An investigation found that a small number of unauthorized users had accessed files between October 2025 and the discovery date. The files contained unencrypted personal information.

“On July 16, 2026, a security vulnerability in a DMDC file sharing system was discovered, which allowed unauthorized users to access files. DMDC immediately updated the file sharing system to patch the vulnerability and the system was restored.” reads a data breach notification letter sent to impacted individuals. “Analysis identified that between October 2025 and the date of discovery, a small number of unauthorized users accessed files on a server containing unencrypted PII. The types of PII involved vary by individual; however, in your case, they include social security number (SSN) and at least one additional identifier such as name, date of birth, contact information, sex, race, and military personnel information (such as occupational specialty).”

The data exposed varies by person, but in this case included Social Security numbers (SSNs) and at least one other identifier, such as name, date of birth, contact details, sex, race or military personnel information, including occupational specialty.

After discovering the vulnerability, the Defense Manpower Data Center (DMDC) launched its privacy and cybersecurity incident response process in line with U.S. government policies and guidelines. The agency says it is assessing the affected system and taking steps to improve its security.

DMDC is also offering 12 months of free credit monitoring through IDX, a company specializing in data breach and recovery services. Individuals affected by the breach are encouraged to contact IDX with any questions and enroll in the service. Enrollment is available through the dedicated IDX website using the enrollment code provided in the notification. The deadline to enroll is August 19, 2027. The credit monitoring is intended to help affected individuals identify potential misuse of their personal information following the breach.

At this time, no known cybercrime group claimed responsibilty for the attack.

DMDC says it launched privacy and cybersecurity incident response actions after finding the vulnerability.

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Pierluigi Paganini

(SecurityAffairs – hacking, US Defense Manpower Data Center)