Al-Qaeda’s main Internet forums have been offline for more than a week in what experts say is the longest sustained outage of the Web sites since they began operating eight years ago.

 

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

The first Web site, Shumukh al-Islam, a primary source for al-Qaeda videos and messages, went down March 22, and since then four others have gone dark. Shumukh reappeared briefly Monday before going down again. A message claiming to be from the site’s administrators said that it would be back up “as soon as possible.”