WASHINGTON -- The way the FBI responded to Jill Kelley's complaint about receiving harassing emails, which ultimately unraveled or scarred the careers of ex-CIA Director David Petraeus and Marine Gen. John Allen, is the exception, not the rule.

The FBI commonly declines to pursue cyberstalking cases without compelling evidence of serious or imminent harm to an individual, victims of online harassment, advocacy groups and computer crime experts told The Associated Press.

But in the episode that uncovered the spy chief's affair, the FBI's cyberdivision devoted months of work to uncover who had sent insulting and anonymous messages about Kelley, the Florida socialite friendly with Petraeus and Allen. She also was friends with an FBI counterterrorism agent in Tampa.

The bureau probably would have ignored Kelley's complaint had it not been for information in the emails indicating the sender knew the travel schedules of Petraeus and Allen, the top U.S. commander in Afghanistan. Instead, the FBI considered it from the earliest stages an exceptional case, and one so sensitive that FBI Director Robert Mueller and Attorney General Eric Holder were notified of its progress.

An AP review of court records found only nine cases in the past two years that identified cyberstalking or cyberharassment as the underlying crime in federal criminal complaints. But the FBI found Kelley's complaint significant. And for good reason, said David Laufman, a former federal prosecutor who handled national security cases. "Most cases don't involve the incumbent director of the CIA or the head of U.S. military forces in Afghanistan."

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Civil liberties groups have criticized the FBI for pursuing the investigation of the emails to Kelley because there is no indication in them of threatening language or classified information.

Federal agencies can obtain a substantial amount of information about the online activities of an individual without getting a warrant from a judge. A subpoena approved by a federal prosecutor is usually sufficient to get access to emails and log-in data.