From Ellen Nakashima and Joby Warrick, the Washington Post:  Al-Qaeda’s main Web forums have been offline for the past 11 days in what experts say is the longest sustained outage of the sites since they began operating eight years ago.

No one has publicly claimed responsibility for disabling the sites, but the breadth and the duration of the outages have prompted some experts to conclude the forums have been taken down in a cyberattack — launched perhaps by a government, government-backed organization or hacking group.

The first Web site, Shumukh al-Islam, a primary source for al-Qaeda videos and messages, went down on March 22, and since then four others have gone dark. The administrator of a second-tier al-Qaeda site recently posted a message on an online forum saying that “the media arena is witnessing a vicious attack by the cross and its helpers on the jihadi media castles. . . .”

There remains uncertainty over whether the recent outages were caused by a cyberattack at all, and some skeptics note that some prominent al-Qaeda forums remain online. U.S. government agencies, including U.S. Cyber Command, had no role in the outages, according to officials who would speak about the issue only on condition of anonymity.

Still, Will McCants, a former State Department counterterrorism official who is now a senior fellow at the Homeland Security Policy Institute at George Washington University, said given the number of sites down and the duration of the outages, “it sure looks like a takedown.”

If it were a technical problem being addressed by site administrators, “usually they will get on another site and say we’ve got administrative problems,” McCants said.

The last lengthy blackout of al-Qaeda Web forums took place in the summer of 2010, when British intelligence officials disrupted the launch of an online magazine produced by the network’s affiliate in Yemen.

In that case, the most prominent al-Qaeda site at the time, al Fallujah Web forum, was dark for at least seven days, said Evan Kohlmann, senior partner at Flashpoint Global Partners, which tracks the sites, which are mostly in Arabic language. The magazine appeared on the restored forum about two weeks later. . . .

Regardless of the cause of the latest outages, if they persist, the larger consequences could be far-reaching, said A. Aaron Weisburd, a senior fellow at the Homeland Security Policy Institute who runs Internet Haganah, a site that tracks jihadi forums.

The loss of primary forums such as Shumukh and al-Fida’ would deprive al-Qaeda of control over its message, he said. “It leaves the rank-and-file to guess which messages and which messengers are genuine al-Qaeda, and provides undercover operators with new opportunities to disrupt the movement,” he said. . . .

In the past, U.S. officials have also relied on diplomatic channels to dismantle extremist sites that are seen as posing a threat to American personnel or interests, according to former U.S. officials familiar with the episodes.

The approach has worked in more than a dozen cases, and in each instance was backed by at least the implicit threat of a cyberattack by the U.S. military if the Web site’s host country failed to act, the officials said. The countries that cooperated were in Europe, the Persian Gulf and the Pacific, they said.

“We’ve never had a country refuse us,” said the former vice chairman of the Joint Chiefs of Staff, James Cartwright, speaking at U.S. China Commission hearing at George Mason University last week. “But if they did, then you can invoke the right of self-defense.” 

Cartwright said that in some cases the foreign government would be given a 48-hour window to investigate, what he termed “fair notice,” before the U.S. military did so on its own.  (photo: Atlantic Wire)  (via @Jason_Healey)