The internet is a wonderful thing, except when it isn't: the greatest communications technology ever invented is often used to spread half-truths, misinformation and outright porkies.
We don't mean little fibs, either, but great big whoppers - we're quite sure there are sites out there claiming that Barack Obama's making measles vaccines in Area 51 to give everybody in Cheshire cancer.
So these are our nominations for the biggest porkies circulating online.
1. All celebrities are deviants
With the exception of - yikes! - The Krankies' swinging, most dramatic celebrity sex stories are untrue: chances are that when you hear that Celebrity X was rushed to hospital with Y in their Z, it's an old urban myth attached to a new name.
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[Image credit: Dudesleeper, CC BY-SA 3.0]
2. Artificial sweeteners are poisoning you
There's a very, very long list of everyday things that are apparently killing us all, from food additives to packaging. One of the most tenacious online scares is the Evil Aspartame one: the artificial sweetener is a neurotoxin that causes cancer, lupus, MS, brain tumours, infertility... you get the idea. Despite endless tests - aspartame is one of the most thoroughly tested food additives the world has ever seen - there's not a scrap of evidence for any of the claims.
3. Wi-Fi is cooking your brain
Wi-Fi uses radiation, and radiation is bad, so Wi-Fi must be bad. Right? Er, nope: there's no evidence that Wi-Fi has ever caused anything to go wrong in anybody's body, and it's highly unlikely that it could: the radiation Wi-Fi produces isn't the dangerous, cancer-causing ionising radiation you get from things such as sunbeds and comedian John Bishop's teeth. It's no coincidence that many sites discussing the alleged dangers of Wi-Fi just happen to be selling products that supposedly protect you from those dangers.
4. Your favourite celebrity is dead
Every few weeks, somebody famous dies. Except they didn't! It was a funny Twitter thing! One day somebody whose death is wrongly announced on Twitter will immediately kill themselves, and the internet will explode.
5. You shouldn't get your kids vaccinated against anything
Anti-vaccination websites aren't just inaccurate - "You have at your fingertips a very powerful tool to find out the facts: the internet," says one anti-vaccine website, with no apparent irony - but dangerous: if you don't vaccinate your kids, they could pass on dangerous diseases to other people. Despite this, celebrities such as Jenny McCarthy help perpetuate misunderstandings, half-truths and outright fictions that put people in genuine danger.
6. Area 51 is full of alien technology, and the moon landings were faked
No it isn't, and no they weren't. Next!
[Image credit: NASA]
7. Barack Obama isn't American
Despite enormous amounts of evidence, many otherwise intelligent people continue to argue that the US President isn't actually American. Of course he isn't: like all politicians he's a shape-shifting Illuminati lizard.
8. America has a giant earthquake gun
Here's a handy truth detector: have Muse ever mentioned it? If the answer's yes, the story's probably bobbins. Muse named a live album after HAARP, the Alaskan ionosphere research programme, because some people believe the whole thing's a front for a giant earthquake gun that also controls our brains and changes the weather. Hang on. Did somebody say weather?
[Image credit: Swampa, CC BY 2.0]
9. Climate change doesn't exist
Some people will look at this summer's awful UK weather, tut, and say: "so much for global warming!" These people are confusing weather, which is what's happening outside your window right now, with climate, which is the pattern of weather over years. Online, much of the "so much for global warming" discussions and posts misrepresent the scientific consensus: our planet is definitely getting hotter, and the overwhelming majority of scientists believe that humans are at least partly to blame.
10. Apple is doomed
Google's released the Nexus 7. Apple is doomed! Microsoft's unveiled Surface. Apple is doomed! The Samsung Galaxy S3 is great. Apple is doomed! Apple has just reported yet another record-breaking quarter of extraordinary profitability! Apple is doomed!
The doom-mongers use two arguments: one, that a new (or better still, yet-to-be-released, or entirely fictional) product will be so good that everybody will stop buying Apple things; and two, that Apple is up against the "law of large numbers", which means it cannot possibly keep growing forever.
The first scenario hasn't happened so far, and the second one won't for a while: as Tim Cook noted earlier this year, despite Apple's success in the phone market "9 out of 10 phone buyers are buying something else". The doom-mongers will eventually be proven right, but only in the sense that a stopped clock is right two times a day.