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.
Marshals spokeswoman Nikki Credic said the agency's computer problem began Thursday morning. The FBI began experiencing similar problems earlier.
"At no time was data compromised," said Credic. The type of virus and its origin were not determined.
In addition to their external networks, most federal law enforcement agencies have an internal-only network to prevent cyber-snoopers from sensitive data.
In Thursday's incident, the Marshals Service shut down its Internet access and some e-mail while staff worked on the problem. The FBI made similar moves to protect its system.