You know something? There's a hilarious video doing the rounds on the internet at the moment. Now, this information obviously won't be forcing understaffed news desks across the globe to coax former reporters out of retirement; if your job involves the use of a computer, you'll do well to get through a working day without being sent a web-link to a video someone thinks is side-splitting.

But, as supposedly hilarious video clips go, this is a pretty good one. It features a well-groomed eight-piece band called Sonseed, all wearing their Sunday best, performing a ditsy little ska tune called "Jesus Is My Friend" on an early Eighties religious show on American TV – and if you haven't seen it, do force yourself to have a look; it's at d95.com/jesus. It has many of the ingredients of a copper-bottomed viral hit: dated haircuts, dubious fashion sense, questionable musical value and, above all, mind-boggling peculiarity.

But there's an equally strange phenomenon occurring on the web these days: a profound disbelief that things are what they claim to be. Wary of being seen as gullible, people simply assume that everything is fake. Within a very short time of the Sonseed video appearing, many had decided that this religious rock band was the brainchild of bloggers hellbent on duping people.

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All kinds of supposed inconsistencies were highlighted: why was the footage in such good condition after 25 years? Why is there no other reference to Sonseed online? Hang on – surely that bass guitar he's playing wasn't in production when the footage was apparently shot? One website, convinced of the veracity of the clip, tracked down the lead singer and interviewed him – but still the doubters weren't convinced. "Nice fake interview," posted one sceptical commenter.

No one wants to be seen to fall for a hoax. It's almost the most embarrassing thing you can do online – on a par with being caught absent-mindedly sucking your thumb on a webcam.

But millions of people fall for online hoaxes every day. Almost every email you receive that warns you about a computer virus is a good example; the renowned "Good Times" email played on our naivety in the early days of the internet, informing us how, if our computers were unlucky enough to become infected, they would immediately enter an "nth-complexity infinite binary loop". Which doesn't exist. Parodies, inevitably, followed: "Good Times will give you Dutch elm disease. It will leave the toilet seat up. It will make a batch of methamphetamine in your bathtub."

But, even today, people fall for similar emails in their millions. Ditto with get-rich-quick schemes; we all know that a surprising number of people are happy to send off money in brown envelopes if they think it'll make them a quick buck. A chap called Dave Rhodes – if indeed he exists at all – used an email known as "Make Money Fast" to dangle the possibility of pocketing $50,000 in 60 days in return for sending out $5 in cash to complete strangers. Needless to say, this unmissable 1 million per cent investment opportunity didn't work; all that happened in 60 days was that you lost $5 worth of your self-esteem.

Pranksters will always play on the gullibility of the majority by setting up hoax websites such as the Online Pregnancy Test (see below) and other sites have achieved greatness and won awards purely because they push the boundaries of satire to the point where it starts to be believed by people. The Onion (theonion.com) blazed a trail in this regard: the Danish television station TV2 was actually taken in by a spoof news story that The Onion ran a few years back, with the headline "Sean Penn Demands To Know What Asshole Took seanpenn@gmail.com".

Part of the fun, of course, is being in on the joke; we desperately want to be part of the savvy group who can look upon the poor, confused idiots who have been taken in with a degree of smugness and self-satisfaction. But that desperation has led to the cry of "Fake!" being heard everywhere.

The "comments culture" of websites these days makes it a piece of cake to accuse people of fakery, and you see it all over the internet – from videos of sleight-of-hand ("Fake!") to first-person accounts of alien abduction ("Fake!"), and from previously unseen photos of terrorist atrocities ("Fake!") to claims of astounding success on gambling sites ("Fake!").

There's very little you can do when someone shouts "Fake!" at you, other than say, "No, it's true, really" – but by that time your detractor will long since have disappeared into the ether, along with his or her staunchly held beliefs. They don't seem to have grasped that shouting a highly sceptical "Fake!" at everything doesn't make them an independent, intelligent thinker – it actually means that they've lost the ability to be sceptical about voices of scepticism.

The colossal popularity of conspiracy-theory websites should probably bear some of the blame for our confusion as to what's real and what's not. It seems to be a badge of honour to suspect any "officially accepted" view of events, and on sites devoted to September 11, the assassination of JFK or the Moon landings, you can see an incredibly skewed rationale for believing a piece of information, with all kinds of dubious sources being perceived as having the same weight. You don't have to have a balanced, rational argument to be taken seriously; you just have to have an argument. So we can see "proof" that Flight 93 didn't crash into a field on September 11, and actually landed safely at Cleveland; and that the London explosions on 7 July 2005 were actually caused by a power surge, with actors hired to play survivors and a demolition company brought in to make the whole thing look convincing.

And throughout these web pages, you will repeatedly see the word "truth" deployed in a range of eye-catching fonts. If you decide that it's the government accounts you believe, you are either a blinkered imbecile or, worse, part of the conspiracy. In short, you can't win.

Scepticism, even cynicism, are healthy attitudes when you're online. But so is common sense – and if we deployed more of it, some of the most infamous hoax sites would never have become viral sensations. But, while we know, deep down, that we should neither believe nor disbelieve everything we see online, there will always be examples that sneak under our radar...

Psycho Ex-Girlfriend

d95.com/psycho

Rambling answerphone messages from hysterical ex-partners are prime candidates for immediate deletion, even before you've reached the bit that says, "To replay this message, press 1," but Mark McElwain rewound, replayed, recorded and immortalised 53 of them on a hugely popular website. Voices of suspicion were raised when attempts to track down the jilted woman failed. The website disappeared not long afterwards and, seven years on, no one really knows whether it was real or just an elaborate way of letting the world know that ladies just can't get enough of Mark McElwain.

The Secret Diary Of Steve Jobs

d95.com/fakesteve

The name of this blog should have dispelled any notions that it might be real, but it took months to unmask the hoaxer who brilliantly lampooned the egotistical reputation of Apple boss Steve Jobs. It wasn't until a book manuscript started circulating that it was revealed to be journalist Dan Lyons – not an Apple insider, as had been thought, but someone who actually had to go out and buy books and biographies to do his research. "My plan at this time is to live forever and to remain in charge here," wrote Fake Steve back in July 2007, "though perhaps with fewer restrictions on my power. The truth is, I am not human – I am a man-god, son of Zeus."

Create Your Own Genetically Healthy Child

genochoice.com

Genochoice doesn't feel any urge to own up to being a joke, preferring instead to tease out any secretly held sub-Nazi views on eugenics from the site's visitors, and allow them to believe for a fleeting moment that it would be possible to mail off a cheque to ensure that their son won't be blighted in later life by male-pattern baldness. I mean, what right-thinking parents wouldn't be willing to cough up $5,875 to "cure" their as yet unborn child from its 98 per cent predisposition to homosexuality? Artist Virgil Wong did a brilliant job on this website in pastiching future medical technology.

Free Online Pregnancy Test

thepregnancytester.com

The net has revolutionised communication, allowed us to buy goods and services from the supposed comfort of our own homes, and has placed a dizzying selection of pornography at our fingertips – so surely it can help us to find out if we are pregnant? Common sense should tell us that the medical scanning abilities of our computer screen are likely to be somewhat limited but, as this site appears towards the top of Google's search results for "pregnancy test", there's no doubt that it has taken a few people in. Note the very light grey writing tucked away in an obscure corner of the site that says, "It's a joke, OK", and maybe get yourself down to the chemist.

Pets? Or Food?

petsorfood.com

You'd have thought, wouldn't you, that a site set up to sell unwanted pets as food – ready-to-eat hamsters, Doberman steaks, exotic Komodo dragons – would be identified instantly as a fake? And of course it's fake – but that didn't stop debate raging as to its veracity among the wide-eyed and pea-brained at such hotbeds of radical thought as Yahoo! Answers. "Is there a way that we can delete the website? That would be a good idea," says one upset animal lover. "I emailed them about it, and apparently it is REAL!" said another. A voice of sanity then pointed out that they supposedly sell dodos. Which are extinct.

Catching Glasses On Your Face

d95.com/sunglasses

Flipping a cigarette from a pack and catching it in your mouth has finally been superseded as the epitome of cool; the new trick is to catch a pair of shades that have been flung casually across the room squarely on the bridge of your nose. How we'd love to believe that this video is kosher, and that it's a trick we could accomplish with a few hours of practice, during which we'd only occasionally be stabbed in the left eye by one of the arms. Sadly, it's a very neatly executed trick involving reversed camera footage and, well, a piece of string. See the full explanation here: d95.com/sunglasses2.

History of a Victorian Era Robot

bigredhair.com/boilerplate

The discovery of evidence relating to Boilerplate, a prototypical robot built in the late 19th century from sheets of iron, pistons and grease, would have been an important moment for historians everywhere had it not been dreamt up by artists Anina Bennett and Paul Guinan. Again, the facts relating to Boilerplate's pivotal role in the Mexican Revolution should have ensured that no one was taken in; but apparently Guinan receives emails from students asking about Boilerplate's means of propulsion, and the robot even appeared in a novel, The Shroud of the Thwacker, after some less than diligent research on the part of the author.

Neiman-Marcus Cookie

d95.com/cookie

The story goes like this: after enjoying some cookies in the cafeteria of her local Neiman-Marcus department store, a woman asked the waitress for the cookie recipe and was told it would cost "two-fifty". After discovering that she had been billed $250 instead of the $2.50 she expected, the customer took revenge by emailing the recipe to all her friends, urging them to spread it far and wide and "stick it to the man". Thing is, Neiman-Marcus never had a cookie recipe (although they have developed one since, in a savvy marketing ploy) and the $250 cookie recipe is merely a cookie recipe. Although it has become the most famous cookie recipe in the world as a result – no mean feat.

Hot Tub Accident

d95.com/hottub

Some virals can't help but furrow brows and trigger debates. This clip of a woman having what you might term an "accident" in a hot tub is too slick to be real. But why would anyone spend time and money setting up a scene of someone defecating in a whirlpool bath? Are they trying to sell us something? What, for goodness' sake? Anti-diarrhoea tablets? Surely not hot tubs? Home insurance? Is it a film trailer? Or what?

Landover Baptist church

landoverbaptist.org

It's not that difficult to satirise the views of far-right Christian fundamentalists such as Fred Phelps (he of "God Hates Fags" fame), but to keep it up for as long as Chris Harper has, creating the ludicrous persona of Pastor Deacon Fred Smith and regularly delivering mock sermons that are posted on YouTube, shows true dedication to the atheist cause. Harper succeeds in provoking fury across the board, from left-wingers who don't get the joke and berate him for his extreme views, to right-wingers who realise that they're being savagely mocked; but the million visitors a month the site receives surely proves that it's working for some people.

So Who Can I Believe?

snopes.com

Named after an irksome family in the novels of William Faulkner, this is a renowned myth-busting, rumour-scotching website that's the first place to go when you want tall tales denied or, more rarely, confirmed. The layout might be hamfisted, decidedly 2001, and long due an overhaul, but the information is extensive, meticulously researched and entertainingly written. Was Houdini really killed by an unexpected punch to the stomach? It would seem not. Is Michael Jackson's phone number contained within the barcode of the album Thriller? Of course it isn't – but that hasn't stopped hundreds of people dialling it on the off-chance; if they'd gone to Snopes first, they could have saved themselves a few cents and a few seconds of embarrassment.

The site was founded by husband and wife team Barbara Hamel and David Mikkelson, who first met online in a discussion forum dedicated to urban myths, folklore and debunking stories of questionable origin. The strength of the site is that it's level-headed, completely unhysterical and considers each story purely on the evidence available. And it's certainly not hellbent on dismissing every possible rumour that circulates – although, in the internet age, more will be baloney than not; it just provides a simple colour-coding of true, false or undetermined, along with references to information sources.

When you see online forums full of tedious speculation on a topic, Snopes comes as a welcome relief because you know you'll be told it straight. Having said that, some people inevitably think that Barbara and David are part of some evil New World Order. But hey, that's the internet for you.

This piece includes extracts from 'Fwd This Link: A rough guide to staying amused online when you should be working' by Rhodri Marsden, published last week by Rough Guides (£5.99)