The U.S. Marshals Service was the victim of a “major” cybersecurity breach earlier this month that exposed a host of “sensitive” law enforcement information, officials told NBC News Monday. The ransomware event occurred on Feb. 17 and exposed “returns from legal process, administrative information, and personally identifiable information pertaining to subjects of USMS investigations, third parties, and certain USMS employees,” a USMS spokesperson told the network. Another official clarified that the Witness Security Program, commonly referred to as the witness protection program, was not affected by the breach. It’s unclear who—or what—was behind the incident, though it remains under investigation.