It was more than twenty years ago that Rick Astley's Never Gonna Give You Up first topped the charts. "Never gonna say goodbye," he crooned in his surprisingly basso voice - and who knew how right he was.

Today we're in a different century, a different millennium, a very different era than the one that first offered up twerpy, earnest, high-waistbanded Astley. But his song, and its video in particular, have found new life in the time of YouTube. Never Gonna Give You Up is at the centre of one of the internet's hottest memes - and if you haven't already fallen victim, it's only a matter of time.

It's called the "rick-roll". You're innocently browsing an apparently useful website and see a link to something else that might be of interest, but when you click through to that destination you instead find yourself confronted with Astley's boyish smile, his manly croon, his awkward 1987 dance-moves.

The link was a fake, a trap, a dummy with the nefarious purpose of... bringing you face-to-face with the ridiculous.

As with so many stupid internet fads, the rick-roll trend had its start at 4chan, a message-board whose lunatic, juvenile community is at once brilliant, ridiculous and alarming. 4chan users had taken to "duck-rolling" each other - tricking one-another into viewing a video of a, er, duck with wheels. In the spring of 2007 some enterprising prodigy branched off from this into the rick-roll. And the rest is history.

The internet began to swarm with rick-rollers - from Slashdot to the World of Warcraft, and certainly to Wikipedia. At YouTube, one posting of the video has had more than seven million views since last May; you can be assured that few of these were intentional. There are online databases of fake rick-roll URLs, and countless jokers have created sham web-browser plugins purporting to block rick-rolls while instead sending visitors to you-know-what.

Of late, however, rick-rolling has begun to permeate the mainstream. It comes mostly courtesy of Anonymous, a diffuse group of hackers and activists who have declared war on the Church of Scientology in an initiative called Project Chanology. Organised without official leaders or hierarchy, Project Chanology manifests itself in Denial Of Service attacks against Scientologist websites, stupid YouTube videos, and in-person protests at Scientologist centres worldwide.

At recent protests in New York, Washington, London and Seattle, masked protesters held up boomboxes and chanted the Stock Aitken Waterman lyrics which Astley made famous. "Never gonna let you down!" they roared, in a live rick-rolling of the Church of Scientology.

Their cleverest move however is at AnonymousExposed.org, a website created this week that perfectly mimics the subtly different Anonymous-Exposed.org, created by Scientologists as an indictment of Anonymous' "cyber-crimes". Of course instead of showing an anti-Anonymous documentary, the mimic site displays - well, we'll let you have a guess.

But the final word goes to Rick Astley himself. Click here to watch our exclusive interview with Astley. The singer, now 42, has forceful words for Anonymous, Scientologists, and all those who have prolonged the rick-roll phenomenon.