Law enforcement computers were struck by a Mystery computer virus Thursday, forcing the FBI and the U.S. Marshals to shut down part of their networks as a precaution.

The U.S. Marshals confirmed it disconnected from the Justice Department's computers as a protective measure after being hit by the virus; an FBI official said only that that agency was experiencing similar issues and was working on the problem. “We too are evaluating a network issue on our external, unclassified network that's affecting several government agencies,” said FBI spokesman Mike Kortan. He did not elaborate or identify the other agencies.