The internet has replaced Middle Eastern camps as the recruiting and training grounds for would-be Islamist terrorists, an expert has warned.
Professor Paul Wilkinson said the al-Qaeda terror network used the web to host an "encyclopaedia" of weaponry, bomb making techniques and tactics.
The extremist websites often use sophisticated security measures.
Prof Wilkinson was speaking as Scottish student Mohammed Atif Siddique was found guilty of distributing terror-related material on the web.
The academic, who works at the Centre for the Study of Terrorism and Political Violence at St Andrews University, has studied extremist websites for many years.
He told BBC Scotland that the propaganda on the sites, much of it written in Arabic, was crude and would fail to persuade any educated and well-informed person.
However, he said it had succeeded in attracting a string of disaffected young Muslims who were eager to sign up for Jihad against the western world.
Prof Wilkinson said: "Al-Qaeda exploits the internet more heavily than any previous terror organisation. They do of course benefit from the fact it is a trans-national medium and they are a trans-national terror network.
"It is from their point of view an ideal means of communication. They use it for propaganda, recruitment and indoctrination with their ideology.
"They have a virtual encyclopaedia of weaponry, guidance on making bombs and tactics that are accessible to people all over the world.
"They don't have to go to camps any longer to obtain a great deal of that practical information."
The professor said it was virtually impossible for governments to police the internet as the extremists simply moved the servers which hosted the sites to another country whenever they felt threatened.
He claimed that many terror attacks had been carried out without any prior warning being picked up by the intelligence services, which suggested that the terrorists' communication systems were extremely secure.
"They use the internet to communicate with each other using encryption and various means of coding which many country's police forces are unable to crack," Prof Wilkinson said.
"They have become very sophisticated. They recognise there is a kind of battle going on between them and the intelligence agencies and police forces and they have remarkably managed to maintain secure communications regarding many of their conspiracies.
Al-Qaeda uses the internet extensively
"They have cleverly used traditional methods as well as the modern technology, for example, sending couriers across a border is probably a more secure way of getting certain information passed from one person in an organisation to another."
Prof Wilkinson said that the websites were "utterly without any remorse or regret for the thousands of innocent people that the organisation has murdered over the years".
He said that many terror groups used their internet presence to attract and groom potential recruits who were felt to be suitable candidates for suicide bombing missions or to fulfil other roles within the organisation.
Prof Wilkinson added: "They back up the use of the internet with people who are trained recruiters and they have continued to find a supply of suicide bombers that outstrips the ability of the intelligence and police services to keep a check on it.
"There are always new faces, people without any record and therefore more difficult for the police and intelligence services to find."