"A co-ordinated cyber-attack made in Al-Qaeda? This has not happened yet, but it is not just fantasy," Dominique Thomas, a specialist in Islamic networks at Paris's School for Advanced Studies in the Social Sciences, told AFP.
"We can envisage it: they have the brains, and the advantage is they don't have to be many to be effective", Thomas added.
Al-Qaeda has so far stuck to classic, if spectacular, attack methods -- the hijackings in the September 11, 2001 attacks and machine gun and bombs.
But on Tuesday top US officials participated in the "Cyber ShockWave" exercise testing responses to a coordinated attack on the Internet, transport, telephone and electricity networks.
And this month US Director of National Intelligence Dennis Blair told the US Senate "terrorist groups and their sympathisers have expressed interest in using cyber means to target the United States and its citizens".
The US defence establishment is also discussing when a cyber-attack on facilities such as the American electricity grid could be considered an act of war.
Online offensives against official websites have already been recorded, including in Saudi Arabia, and the necessary expertise is available on some forums.
"On jihadist websites there are all sorts of manuals explaining how to make an e-bomb, how to create a virus, how to use encryption techniques", Thomas said. "They are very up to date. The Saudis especially are very strong."
Among militants indicted for terrorist acts, there are more students from pure sciences such as mathematics or information technology than there are from the social sciences, according to numerous studies.
Nigerian, Umar Farouk Abdulmutallab, who is accused of trying to blow up a US bound jet on December 25 studied mechanical engineering at a top London university.
James Lewis from the Center for Strategic and International Studies who co-authored the "Security in cyberspace in the 44th presidency", said a cyber-attack was only a matter of time.
"Al-Qaeda doesn't yet have the kind of capabilities to pull off the kind of big disruptive attack that they really want," he said.
"But over the next few years, they will develop these capabilities."
"We have to expect something big to happen within a decade", he said.