Al-Qaeda Web Forums Abruptly Taken Offline

"Oh, my God, save my brothers on the jihadi forums," one user posted on al-Hesbah, according to Kohlmann.

"My dear brothers . . . increase your supplications for Allah to guide the bullet and to restore al-Ekhlaas successfully so that the message is spread," another user wrote, according to SITE, referring to the most prominent of the downed forums.

Johnsen said that on extremist "forums that are still up, you have people who are quite paranoid and quite confused" about what's going on. He said it is "certainly normal for jihadi chat rooms and forums . . . to have some kind of disruption. It was very clear this is something entirely different."

Al-Qaeda has continued posting videos and statements on al-Hesbah. But Kohlmann said comparatively few followers have passwords to that site.

Al-Qaeda webmasters may be too concerned about letting in infiltrators to issue more passwords for al-Hesbah or to move to an alternate forum with new passwords, Kohlmann said.

"It's the first time it's happened now in three years for al-Qaeda to have only one forum left carrying al-Qaeda's propaganda stream," Kohlmann said. The al-Fajr center was created in late 2005.

Al-Qaeda has had to rely on the sites of others to help distribute its videos, costing the organization some control of its message and shrinking its audience, monitors said.

The sabotage of sites operated by extremist groups makes it more difficult for those groups to inspire attacks and recruit attackers, said Erich Marquardt, editor in chief of the Sentinel, a monthly online publication by the Combating Terrorism Center at the U.S. Military Academy at West Point.

However, "the downside of knocking jihadist Web sites offline is that you lose the ability to monitor jihadist activities," eliminating opportunities for Western monitors to search for ideological weaknesses or clues to future operations, Marquardt said. "When these Web sites are taken offline, it closes an important window."

Separately, Sunni and Shiite Internet partisans are waging a tit-for-tat hacking war. For now, Sunni extremist sites are taking the brunt.

In September, hackers targeted what Iranian news media estimated to be 300 Shiite sites, many of them operated by Shiite religious leaders in Iran. Targets included the official site of Grand Ayatollah Ali Sistani, the leading Shiite cleric in Iraq. For several days, visitors to that site were connected instead to a YouTube video featuring American talk-show host Bill Maher mocking what he said were the cleric's edicts, or fatwas, on sexual matters. Aides to Sistani later denied that he had issued such edicts.

A group called Ghoroub XP, based in the United Arab Emirates, asserted responsibility. Its claim has not been publicly confirmed by any authorities.