Forget about firewalls and extra security. It turns out that even the FBI can get hit with a virus.

The bureau confirmed last week that it was forced to shut down its Internet-facing unclassified network, but denied a report that the agency was unable to email other intelligence and law enforcement agencies.

"The external, unclassified network was shut down by the FBI as a precautionary measure," the FBI said in a statement. "Within 48 hours of identifying the issue and mitigating risks, email traffic was largely restored to the external, unclassified network."

Computerworld quoted a source saying that FBI agents were able to send email on the agency's more secure internal network or use their BlackBerry handhelds.

"We can email to anyone...and [we] have Internet access. We also have a secure email system that connects all 400-plus offices around the country and 60 offices overseas," FBI spokesman Paul Bresson said in an email message.

However, this kind of incident can happen at any agency, and many have faced an email blackout caused by hackers. The question now is how will an agency like the FBI, which has plenty of intelligence data in its system, prevent it from happening again?

In the FBI's case, the agency said it was blocking users from sending or receiving attachments on the unclassified network to give its technicians time to make sure the threat has been blocked. But what happens next time?

For more on the FBI's email problems:
- check out this Computerworld article