Al Qaeda is reported to have been on the receiving end of a suspected organised cyberattack after a clutch of important propaganda websites suddenly disappeared from the Internet two weeks ago.

The five affected sites – including core sites al-Fida and Shamukh al-Islam - were suddenly unavailable on 22 March, silencing the stream of ‘official’ press releases that have been issued by the organisation via the Internet since 2003.  

A less important site returned after three days since when only one other site had managed to reappear but without posting new content.

"Al Qaeda affiliates in Pakistan, Yemen, Iraq and North Africa haven't had any releases since then [22 March]. I don't remember a time when it's been 11 days between releases," Brandeis University Jihadi researcher Aaron Zelin told the Christian Science Monitor.

The Jihadi sites’ administrators have blamed it enemies for the takedown, reportedly posting a comment on a third party site referring to the attack.

“The media arena is witnessing a vicious attack by the cross and its helpers on the jihadi media castles,” it said.

Who might be behind the downing remains a mystery although The Washington Post reported sources in the US intelligence services as denying involvement.

However short-lived, the attacks appear to have had some effect on the loose organisation served by the sites.

“At least temporarily, the social networking among jihadists has been disrupted. The remaining forums are really struggling to attract the participation of users,” The Washington Post quoted Evan Kohlmann of monitoring outfit Flashpoint Global Partners as saying.

Despite longstanding predictions of sophisticated terrorist use of the Internet, the available evidence suggests that radicals are probably more vulnerable to cyberattack than the large intelligence organisations they vehemently oppose.

The websites are probably as avidly consumed by the organisation’s enemies as their supporters who nevertheless depend heavily on the Internet to receive a diet of propaganda videos and documents.

Sometimes the lack of sophistication is by design. After the death of Osama bin Laden, the primary communication system he used was revealed to be encrypted messages stored on huge numbers of USB sticks.