About a dozen uniformed police in riot gear, and a handful of detectives, gathered outside the four-storey terraced house on a quiet street just off Shepherds Bush roundabout in West London.

After a tip-off from overseas colleagues, they knew that inside was a man in contact with a group planning a bombing in Central Europe. His name was Younes Tsouli, but the detectives knew little more about him.

As they tried to shove their way in, the young man in the top-floor flat forced his door shut. It didn’t hold for long. Once the police flooded in, there was a struggle. A mirror smashed and one officer emerged bloodied from a shard of glass. Tsouli was overpowered. “He was thoroughly detained,” one detective recalls. At first, officers were not sure that they had the right person: the long-haired young man in jogging shorts bore little resemblance to the short-haired man in the photo they had been given. But when he confirmed his name, they knew they had their man. Two detectives led him away.

Amid the mess typical of any 22-year-old’s room, detectives found a laptop on a desk, still switched on and with programmes running. When specialist forensic science officers arrived, they found that Tsouli had been creating a website called YOUBOMBIT. A banner with the title and flames was across the bottom of the screen. Also on his screen was a search box with the word “bomb” as the search term. Tsouli was logged in under the username IRH007. The detectives didn’t know it – and wouldn’t realise for some weeks – but they had caught one of the most notorious, most wanted cyber-jihadists in the world: a man whose case illustrated perfectly how terrorists are using the internet not just to spread propaganda, but to organise attacks.

Younes Tsouli arrived in London in 2001 with his father, a diplomat from Morocco. He studied IT at a small college in Central London. With few friends, he soon immersed himself in the world of the internet. Online images of the war in Iraq radicalised him. In his mind it was evidence of a war against Muslims. Soon he was in the darker areas of the net, and graduated from viewing images to publishing them. He used variations of the username Irhabi 007 – irhabi meaning terrorist in Arabic, and 007 being a reference to Britain’s most famous fictional spy.

From 2003 he joined web forums and built a reputation for publishing material such as manuals on hacking. By 2004 he was posting extremist videos and propaganda. That was when he came to the attention of al-Qaeda leaders in Iraq, who spotted his potential. They were making videos but struggling to get them to a wider audience because of the size of the files and the difficulty of finding websites that could host them.

Tsouli solved this problem, making him invaluable. He was e-mailed links that allowed him to download videos from a server. He converted the material into various formats, including one that allowed the videos to be watched on mobile phones. The videos were then uploaded to web pages so that a wider audience could see them. This was often done by hacking into and “hijacking” websites, whose creators didn’t realise that they were hosting terrorist propaganda. Tsouli even managed to post videos of Osama bin Laden on an official website of the state of Arkansas. The videos he uploaded included some showing the kidnapping and murder of hostages in Iraq, such as Nick Berg.

Evan Kohlmann, an expert on cyber-terrorism who gave evidence at Tsouli’s trial, explains: “007 came at this with a Western perspective. He had a flair for marketing, and he had the technical knowledge and skills to be able to place this stuff in areas on the net where it wouldn’t be easily erased, where lots of people could download it, view it and save it.”

Tsouli’s work was certainly appreciated.

Representatives of Abu Musab al-Zarqawi, al-Qaeda’s leader in Iraq until his death in 2006, issued messages of support for Irhabi 007. “May Allah protect you,” one read.

In August 2005 Tsouli became administrator of al-Ansar, a password-protected web forum where extremists communicated with each other. The forum’s 4,500 users networked and shared practical information: some of the links were to instructions on making explosives. Among the discussions were details of how to get to Iraq to be a suicide bomber. Tsouli’s message boards created contacts that would otherwise have been impossible. Kohlman says: “007 was working essentially as a matchmaker, setting up would-be suicide bombers with al-Qaeda in Iraq.” One message read: “I’m ready to run off but I’m under 18. Am I too young?” The chilling reply was: “They have no objection to age.”

Tsouli’s skills began to attract more than just al-Qaeda: a group of cyber-trackers – private individuals who monitor extremist websites – began to take notice of the new kid on the block. One of the trackers was Aaron Weisburd, who operates from a secret location in the US. He spotted Tsouli on a forum called Islamic Terrorists and, like others, he thought at first that anyone using the name Irhabi 007 had to be a joke. He says: “At first I started publishing bits and pieces of what he was doing online for comic relief, and really had no appreciation of where he was headed.” Soon, however, Weisburd realised that whoever the mysterious cyber-jihadist was, he posed a real threat. Tsouli began carrying out intelligence work for al-Qaeda: for instance, looking for home movies from US soldiers serving in Iraq that would reveal what the inside of a base looked like, so future attacks could target weak spots.

Weisburd began not just tracking Tsouli’s work but communicating with him on the internet. “Because I knew he was monitoring me, I would post messages to him just to sort of tweak him,” Weisburd explains. “I would give him a message like, ‘Your days are numbered – you’re going to get caught’. He, on the other hand, was participating in discussions about which part of my body they wanted when I was killed, and he said he wanted one of my fingers as a souvenir.”

Despite the threats, Weisburd kept going. And Tsouli began to get sloppy, failing to do enough to hide his IP address (the unique number that identifies a computer). This meant that Weisburd was able to triangulate Irhabi 007’s rough position in 2004 – and, to his surprise, the nearest internet router to Tsouli was in Ealing in West London. Weisburd’s information was passed to the authorities, but they still couldn’t find the elusive cyber-jihadist, who was now being hunted by intelligence and law enforcement agencies from across the West.

When London was bombed in July 2005, Tsouli wrote: “Brother, I am very happy. From the moment that the infidels cry, I laugh.” He grew enamoured of his own reputation, and kept a cutting from the New York Post from September 2005 that read: “U.S. SHAKEN BY QAEDA 007”. In a message dated June 5, 2005, he wrote: “I am still the terrorist 007, one of the most wanted terrorists on the internet. I have the Feds and the CIA, both would love to catch me, I have MI6 on my back.” But as his ego and ambitions grew, so did his chances of getting caught.

What makes Irhabi 007’s case so chilling is the evolution from simply setting up websites to becoming involved in terrorism itself. Increasingly he pined to go to Iraq to fight, and increasingly he became involved with others who were planning attacks. Two men who chatted with Tsouli online travelled from Atlanta, Georgia, to Canada to meet a group of extremists whom they knew from Tsouli’s forums, and then to Washington, where they took what are alleged to be reconnaissance videos of targets such as Capitol Hill. These videos were later found on Tsouli’s computer.

It was Tsouli’s links to a planned attack that brought the police to his door in October 2005. In a deliberate echo of 9/11, a group calling itself al-Qaeda in Northern Europe posted a declaration on al-Ansar at 8.46am on September 11, 2005. One of the men behind the declaration was 18-year-old Mirsad Bektasevic, who called himself Maximus. After publishing the declaration he travelled from his home in Sweden to Bosnia. In a house in the suburbs of Sarajevo he and an accomplice filmed a chilling suicide video. Surrounded by weapons and explosives, including a suicide vest, they say that they are preparing for attacks against those who have troops in Iraq and Afghanistan.

What they didn’t realise was that they were under surveillance. On October 19 the Bosnian police arrested them. Bektasevic’s phone records showed that one of his last calls was to West London. The Metropolitan Police were informed and moved on the address in Shepherds Bush. They had no idea when they arrested him that Younes Tsouli was also Irhabi 007: they simply believed that he was linked to the men in Bosnia, and therefore potentially dangerous.

After Tsouli’s arrest, police spent five days searching the flat, tearing up the carpets in a search for evidence. Items such as computer thumb drives could be hidden anywhere. But it was only when they started to pick apart the files on Tsouli’s computer that they realised what they had. There were some obvious signs, such as the Powerpoint-style presentation on how to build a car bomb. But as the team dug deeper, scouring through two million files, they realised that there was much, much more. Some of the files were encrypted, others in Arabic. One clue was that there was no pornography, which they usually find in abundance – except on the computers of terrorist suspects.

A professor of computing built virtual computers for each of the investigators, so that they could work on the files independently. As officers started looking at the archived information from chat forums and the edited video files, the penny began to drop: Tsouli was a major player. There could have been more, but Tsouli had just reformatted one of his other computers, erasing much of the information and leaving only fragments for detectives to work on. But crucially, in the flat they found a piece of paper with a list of websites that Tsouli had set up using credit cards and different identities. He had kept it as a reminder, but it was to prove damning.

In the end, the evidence was enough to force Tsouli and his codefendants to change their pleas to guilty halfway through their trial last summer.

In December, Tsouli’s sentence was increased from 10 to 16 years. His conviction was the first for incitement to commit an act of terrorism through the internet, and a sign of what terrorists are capable of. “What it did show us was the extent to which they could conduct operational planning on the internet,” Peter Clarke, the head of the Metropolitan Police Counter-Terrorism Command, told me. “It was the first virtual conspiracy to murder that we had seen.”

The power of the internet is its ability to put like-minded people in touch from every corner of the world. But the benefits for terrorists can also be an advantage for detectives when they catch a suspect, because they can quickly trace the people with whom the suspect was in contact.

“Once you get on to one guy who’s important in a network, because the structure of a network is flat . . . you get everyone he’s connected to,” Aaron Weisburd explains. “In the old days a terrorist organisation would have a much more hierarchical structure, you would have tight little cells and one guy would know maybe one person one step up and maybe one person one step down, but that’s it. In a network structure, if you get the right guy the whole thing goes down.”

That’s exactly what happened with Tsouli. His arrest has been linked to a series of others around the world, including the arrest of 17 men in Canada in June 2006 and the two Americans who travelled to Washington. There have also been arrests and convictions here in the UK of individuals who visited Tsouli’s web forums.

Others have tried to take Irhabi 007’s place, even paying homage to him and using similar names. But no one has been able to fill his shoes and al-Qaeda has been forced to use teams of people to replicate what that one young man did from his bedroom in Shepherds Bush. No one has matched his influence on the web: they have learnt to keep a lower profile than the celebrity-conscious Tsouli. “Keep in mind, those were some pretty big shoes and his name is still being talked about on the internet now like he’s a god,” Evan Kohlmann says.

The cat-and-mouse game continues: one in which the teenage and twentysomething supporters of al-Qaeda often have the upper hand over law enforcement and intelligence officers, who often come from a different, less computer-savvy generation. But for other wannabe internet terrorists, the cyber-trackers are still out there. As Aaron Weisburd puts it: “If you’re a terrorist and you’re dependent on the internet, I have bad news.”

— Terrorist 007 is on Newsnight on BBC Two tonight at 10.30pm, and on Our World on BBC News24 on Saturday (2.30 and 9.30pm) and Sunday (2.30pm)

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