The FBI's computer woes got even worse last week when bureau officials were forced to shut down a commercial e-mail network used by supervisors, agents and others to communicate with the public. The reason, sources tell NEWSWEEK, was an apparent "cyberintrusion" by an outside hacker who officials fear had been tapping into supposedly secure e-mail messages since late last year. FBI spokesmen publicly sought to downplay the damage, saying the compromised commercial server--maintained by AT&T--was used exclusively for unclassified and "nonsensitive" communications that did not involve ongoing investigations. One example, they said, was notices from public-affairs offices' fbi.gov addresses to members of the press. But privately, officials were highly concerned--and recently notified the White House. One top FBI official says he regular-ly used his shut-down fbi.gov e-mail account to send messages to state and local police chiefs. Another source tells news-week that more than 3,000 old and current e-mail accounts were shut down. Others say the same apparently compromised server also provided accounts to other government agencies. Justice Department officials, who launched their own cybercrime investigation into the apparent intrusion, noted that there was no telling the potential damage at this point, given the common tendency for everybody to say too much--including making references to law-enforcement "sensitive" cases--even in theoretically routine e-mails. "This is an eye-opener for all of us," says one FBI official.

The bigger question, sources say, was how the hackers penetrated the bureau's e-mails--and why it took the FBI so long to notify the rest of the government. The FBI e-mail system was erected with firewalls that were supposed to prevent even sophisticated hackers from penetrating. But while officials stressed there was no evidence that the apparent intruder or intruders were part of any terrorist or foreign intelligence organization, the authorities were still baffled as to how they got into the system. According to sources familiar with the investigation, one suspicion is that hackers either used sophisticated "password cracking" software that tries out millions of password combinations or somehow eavesdropped on Internet transmissions. Over the weekend, NEWSWEEK has learned, the Department of Homeland Security posted a computer-security alert to agencies throughout the federal government urging e-mail users to be more careful about choosing their passwords by avoiding obvious clues--like nicknames, initials, children's names, birth dates, pet names or brands of car. "Such information can be easily obtained and used to crack your password," the bulletin states.

The e-mail compromise couldn't have come at a worse time for the bureau. Just last week, the Justice Department inspector-general released a report sharply criticizing the FBI's management of its new Virtual Case File computer system--a $170 million software upgrade that bureau officials now concede they may have to --scrap. The VCF system was supposed to make it much easier for agents to electronically access vital information relating to ongoing cases in different FBI offices. But the I.G. found that poor planning and ineffective management have resulted in a system that is nearly unworkable. FBI chief Robert Mueller, who sources say has personally briefed President George W. Bush on the matter, took responsibility "at least in part" for the fiasco before a Senate subcommittee. "No one is more frustrated and disappointed than I," he said.