A Mystery computer virus infected FBI and the U.S. Marshals computers forcing them to shut down part of their networks as a precautionary measure.

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.

Both Federal law enforcement agencies shut down its Internet access to protect data.

U.S.