There were signs, if you knew where to look, that the launch of Operation Sea Arrrgh was imminent. In a hundred corners of the internet plots were being plotted; in fancydress shops sales of Guy Fawkes masks were rising and in thousands of dank teenage bedrooms young men and women were making plans to converge on sites around the world, dressed as pirates.

Their target was the Church of Scientology - and this was an altogether new way of protesting. It was all so different from how it used to be. For more than a decade, a small group had gathered opposite the Church's London offices to stage lonely demonstrations. Some were former Scientologists, some just angered by an organisation that they claimed split up families, extorted money and employed its followers as slave labour. Leafleting passers-by, explaining themselves to the police and countering - they claimed - the harassment of the Scientologists, they were happy if a dozen turned out.

Then, earlier this year, something odd happened. Simultaneously and apparently without warning, in London, Toronto, Sydney, New York and other cities worldwide, young men and women began protesting en masse. They wore strange clothes, spoke their own dialect, distributed cake and operated under the name of Anonymous. They returned the next month - and the month after.

Who were these people? To the police, watching last Saturday's London protest, they are a quirky bunch of middle-class kids. “These are the nicest protesters I have ever had the privilege of policing,” one said. “They even bring lunch.” Sure enough, behind the barricades, there is a large table of crisps and soft drinks. Demonstrators offer biscuits to passers-by. One of their placards reads: “We have cake, they have lies.” The police description is broadly accurate - most Anonymous members are indeed middle-class teenagers. They see themselves as guardians of free speech, fighting a malign organisation that bases its ideology on stories about aliens. They cover their faces because they are scared of reprisals. But also because anonymity is, well, what they do.

Why, though, has a bunch of young people, connected only by the internet, decided to target a US religion started 50 years ago by a science-fiction writer? Why not the Iraq War, nuclear weapons or climate change? One answer is that they believe they can achieve something with Scientology. The most realistic of Anonymous's aims is to revoke the group's tax status - it is exempt from some VAT payments and receives rebates on other taxes. But the point is moot. You might as well ask why their most popular song is Never Gonna Give You Up, a 1987 hit by Rick Astley, or why they laugh at pictures of cats. And why are most of their masks a depiction of Guy Fawkes from the film V for Vendetta? Internet memes are not always logical.

It all began as a running gag. The default name for new members on message boards is often “anonymous”, and someone suggested that maybe anonymous could be a real person. People began acting as one and the idea went viral. “We are the hive mind, the anger that leaked from the computer screen,” explains a long-haired twentysomething with an eye patch, standing in the June sunlight last week. “The cult failed to understand how things arise out of a mass consciousness, and now they have kicked the hornets' nest. What you are seeing here is the emergence of a new kind of democracy.” The internet is the one element that has dictated the nature of Anonymous, allowing informal membership, and a leaderless organisation structure barely recognisable from the protest movements of old. “The common assumption today is that young people are apolitical, disengaged, hedonistic and only interested in partying,” says Bart Cammaerts, a lecturer in media and communications at the London School of Economics. “This is wrong. The internet is not a guarantee of success, but it has allowed people to inform, recruit, mobilise and organise.”

Anonymous's initial activities were silly - playing tricks or hijacking forums. Some were borderline legal. They would bring down websites by bombarding them with data (“distributed denial of service”). “Frankly, it wasn't very noble. But it was fun,” explained one Anonymous, who called himself Halfdark. They have a word to describe such activities - lulz (see panel). Early this year, a video was posted online of Tom Cruise discussing Scientology. Unintentionally funny in its sincerity, it spread across the internet. Scientology called in the lawyers, and began forcing sites to remove it. Anonymous had a target.

“They had started screwing with the internet,” said Marc Abian, named afterthe Scientologists' belief in an evil race of aliens called the Marcabians. “Initially we harassed them for lulz, but then we realised that they ruin lives. What we do is fun, but with a real cause.”

Last Saturday targeted Scientology's elite Sea Org - a pseudo-paramilitary group that used to own a ship. Hence the pirate costumes and the name - Operation Sea Arrrgh (as in “Arrrgh, me hearties”). “We get asked: ‘Why can't people believe what they want?'” said a young woman, holding a plastic cutlass. “The answer is, we are not targeting the beliefs, but the Church. Why does it take people's money? Why does it split people from their families? It is a dangerous cult.” As she spoke, a chant began. Pointing alternately to Scientology's UK headquarters in Blackfriars, London, and the next-door Church of Saint Andrew by the Wardrobe, the crowd cheered: “This is a cult, this is a church. This is a cult, this is a church.” A few tourists laughed, the policemen shuffled. It was, oddly...cultish.

At first, Anonymous kept their previous tactics - but they were counterproductive as Scientology could say that it was the victim of a bullying campaign. So Mark Bunker, a prominent critic of the Church not associated with Anonymous posted a message on YouTube asking them to work within the law. Bunker argued that their actions were damaging the work of campaigners such as him and websites like xenu.net. Anonymous listened. They now revere Mark Bunker as Wise Beard Man (“his words are wise, his face is beard”). When I asked the police on Saturday if they were expecting trouble, one laughed. “They aren't a problem,” he said. “I just wish that they'd stop playing that bloody Rick Astley song.” Just before lunchtime, the protest shifted to a smaller Scientology centre on Tottenham Court Road. And so we set off on the Tube - pirates, dancing to the theme tune from the cult 1990s US comedy Fresh Prince of Bel Air. We were a conga line composed of internet memes.

Rarely, though, has there been a more polite mob. We had leaflets, we explained ourselves to tourists and everyone seemed to take it as fun - even when a train was boarded to the pirate cry “We be commandeering this vessel!” The “Dianetics and Scientology life improvement centre” on Tottenham Court Road, probably feels less charitable. Talking over Rick Astley, the Scientologist inside handed me a leaflet on the founder L. Ron Hubbard's masterwork, Dianetics: The Modern Science of Mental Health. “To be honest, they probably just give us extra publicity,” she said.Here, instead of a church, there was a KFC, and the chant morphed to “Chicken. Cult. Chicken. Cult.”

Around the corner, Epic Nose Guy granted me an interview. He wears a long-nosed Venetian mask and is the closest thing that Anonymous has to a celebrity. Two months ago, he very nearly appeared in court - after he held up a placard calling Scientology a cult. His case was taken up by Liberty, the human rights group, and was even championed in this paper.

“I believe in freedom of speech, so I made a big sign saying ‘Scientology is not a religion, it's a dangerous cult'.” He smiles. “Within ten minutes, the police asked me to take it down, but I ignored them. If you give away your right to say what you want on a sign, you're giving away your right to protest, full stop.” So he was presented with a court summons. The case was dropped but he must have been worried? “Absolutely. It was scary - I was in the middle of my GCSEs.”

We're in it for the 'lulz': understanding the lingo

Caitlin Moran

As human beings, our concept of how things get done is based around heroes. Che Guevara. William Wallace. Guy Debord. History's fulcrums. Leaders. This, then, is why Anonymous is such a thrillingly novel thing. Anonymous has no heroes. It's just a sniggering swarm of geeks with an arsenal of slang and fire in their bellies.

Initially, it was the slang that drew me into Anonymous, through the affiliated websites 4chan and Encyclopedia Dramatica. As a woman with three teenage brothers, I wanted to know why they kept shouting “I WONZ you, n00b” and why, if I mistimed a gag, they said, witheringly, “Rofl”. I found out they were getting all their new words from Encylopedia Dramatica. They were speaking “l33t-speak” - a slang developed on chatboards and multi-roleplayer games. It plays more with the look of words than the sound. Meaning is altered with intentional typos (”moar” is ultra-more). Acronyms are huge: GTFO (get the f*** out), ROFL (roll around on the floor laughing), IRL (in real life), ZOMG (oh my god) - but all are used with weary irony. Additionally, there are in-jokes (LOLcats) and lodestone quotes from games and films - “Epic win”, “Goodnight, sweet prince”, or “Tonight, we dine in HELL”. The key word, however is “lulz” - an acronym that has been fleshed back out into a word. Like “Hakuna matata” in The Lion King, “lulz” is not just a word, but a philosophy. Lulz are the laughs that you get when you do something unexpected and possibly slightly wrong - partly to amuse others, but, most importantly, to amuse yourself. As Encyclopedia Dramatica explains: “Johnny Cash became the ultimate lulz pioneer with Folsom Prison Blues and the lyrics: ‘I shot a man in Reno, just for the lulz'.” And it is the lulz that are Anonymous's great weapon. For it would be easy for Scientologists to fight back if they were being attacked by a single, heroic, Michael Moore-type. But no one has ever had to fight geeks dressed up as pirates.

Anonymous has made campaigning sexy for the first time since 1968. The lulz is, after all, the ancient spirit that once made the young become Marxists, or sail off to the New World. Now it's been rediscovered by a bunch of World of Warcraft fans with a grudge against Tom Cruise. Epic win, as they would type, with a sarcastic sigh.

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