Hackers earlier this month maliciously encrypted a system belonging to the U.S. Marshals Service, compromising and exfiltrating sensitive data law enforcement data.

Department of Justice officials classify the attack as a “major incident,” said NBC, which broke news of the attack.

Exposed data include returns from legal process, administrative information and personal identifiable information pertaining to subjects of USMS investigations, third parties and a few USMS employees. NBC reported the breach did not affect data of individuals in the Witness Security Program, which relocates witnesses whose cooperation with prosecutors endangers their life or their families’ lives.