A misconfiguration in the bureau's domain name setup meant that many visitors to FBI.gov could not get through. As of 11 a.m. PT, the FBI's configuration problem had been fixed.
The apparent error also wiped out the online presence of the FBI's high-tech crime unit, the National Infrastructure Protection Center, at NIPC.gov.
An FBI spokesman said earlier Tuesday that the glitch was accidental and was not the result of a malicious attack. "The server is down," said Paul Moskal. "It's an internal issue here. That's the good news, as opposed to some attack or something."
Early on Tuesday, the FBI's domain name servers started sending empty replies when visitors tried to reach the site. Some Internet service providers kept a temporary copy of the correct information, meaning that FBI.gov and NIPC.gov were occasionally reachable.
The FBI receives its Internet connectivity through Akamai, a Cambridge, Mass.-based company with about 13,000 servers that store data on behalf of clients.
"This has nothing to do with the services that Akamai provides FBI.gov," said Jeff Young, a spokesman for Akamai. "We obviously are continuing to support them however we can."
Jon Lasser, a Baltimore-area system administrator and author of "Think Unix," said the FBI's mistake was likely "some sort of server misconfiguration. Their host stopped returning the addresses of their Web servers. That's not good."
Easily recognizable names like FBI.gov are translated into numeric addresses through the Domain Name System (DNS).
Microsoft made a similarin January 2001 that knocked out its Web sites for a full day. An embarrassing series of problems centering on a collection of routers in Canyon Park, Wash., took out dozens of Microsoft properties including Hotmail.com, MSN.com, Microsoft.com, and MSNBC.com.
Moskal blamed the bureau's woes on "an internal crash that we all experience occasionally."