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.