Conspiracy theorists seem to come in two flavours - there are those apparently intelligent people who are extremely passionate about what they see as massive cover-ups and frauds. Then there are the fringe-dwelling nutters who wear tinfoil hats to keep the satellites from spying on them.

But in the internet era there's more than enough fodder for paranoid bloggers and way-out webmasters to sink their dentures into.

A video posted on YouTube showing Michael Jackson emerging from a coroner's van has just been revealed as an experiment to show just how quickly suspect theories can be spread across the web. Quite quickly, it would seem, with 880,000 hits on the hoax clip in just one day.

Here's our selection of the best, or should that be worst, conspiracy theories ever.

1. 9/11
There are people who believe that the September 11 attacks on New York's World Trade Centre and the Pentagon were either orchestrated by the American government and that well-respected genius George W Bush, or simply allowed to happen.

The web is bursting with variations on that theme, including claims that the Pentagon damage was caused by a missile fired from inside the building and that no wreckage from the American Airlines 757 was found at the scene. Read more here and Popular Mechanics' debunking of the theories here.

The main Trade Centre theories are focussed on pre-existing knowledge of the pending terrorist attacks, and that the towers were taken down by controlled demolition rather than as a result of the planes hitting the building.

2. Moon landing
The 1969 Apollo 11 moon landing was a big fake, some say, with the US staging the whole exercise to appear as if NASA beat Russia in the lunar landing race.

Non-believers point to anomalies like shadows going in different directions and the US flag fluttering in the moon's non-existent wind to prove their theories.

Astronaut Buzz Aldrin doesn't take kindly to these moon landing conspiracy theorists, and can be seen on YouTube punching a guy in the face.

Read all of the lunar theories here.

3. Princess Diana murder
After Princess Diana and her boyfriend Dodi Al-Fayed were killed in a Paris car accident while being pursued by 'paparazzi', rumours and theories did the rounds that the Royal Family were responsible for her death.

Claims included one that Diana was pregnant to Al-Fayed and was planning to marry him, raising the ire of the royals. Another said that M16 saw the relationship as a threat to the throne and took the much-loved princess out.

A good round-up of Diana theories can be found here.

4. Area 51 and Roswell
UFO sightings are often by country bumpkins from small towns in the middle of nowhere, like the thriving metropolis of Roswell, New Mexico. It was here that a UFO supposedly crash-landed back on July 8, 1947.

Trailer park-dwelling gents with glorious mullets and names like Cletus say the US military's claim that the flying saucer was nothing more than a weather balloon is rubbish and that parts of the alleged spacecraft were recovered from the scene. Some even say that extra-terrestrial bodies were also found.

The 'top secret' Area 51 base at a former nuclear test site in Nevada has long been rumoured to house everything from spaceships to little green men. Some believe that the US government has reverse-engineered, built and tested flying saucers at Area 51.

5. Alternative energy sources
We could be running our cars on water and powering our cities with fairy dust, if many theories on energy cover-ups are to be believed.

Scientific discoveries have supposedly been suppressed by oil companies, power companies and governments, which any reasonable person would think is highly likely.

In the science world, many free energy claims are dismissed as impossible under currently accepted physical law - like perpetual motion machines and zero point energy.

6. Who is controlling Earth?
There are numerous theories on who - or what - holds sway over the world's financial systems, including the publicity-shy Bilderberg group and the traditionally secretive Freemasons.

One of the more outlandish suggestions is supported by former footballer and outspoken conspiracy theorist David Icke, who tried to reveal the 'truth' in his 1999 book The Biggest Secret: The Book that Will Change the World. He thinks that the planet is in fact run by race of alien lizards from the Draco constellation. The lizards have cross-bred with humans, he reckons, to create reptilian human hybrids that have included the Queen Mother, Hillary Clinton and George Bush Snr.

7. JFK assassination
Who killed John F Kennedy? According to the tinfoil hat brigade, it could have been the CIA, the KGB, organised crime, J Edgar Hoover, Castro, Richard Nixon or Lyndon B Johnson.

When he was shot while part of a motorcade in Dallas on November 22, 1963, the world went into shock as the rumour mill started to find overdrive. Was Lee Harvey Oswald on a government payroll? Was Jack Ruby paid to assassinate Oswald to cover it all up?

There are said to be piles of CIA documents under semi-permanent lock and key which will one day reveal all. This comprehensive site attempts to debunk the vast number of Kennedy assassination theories.

8. Microsoft 'Wingdings' messages
When Windows 3.1 was released in 1992, some genius discovered that the bundled Wingdings font was harbouring hidden anti-Semitic messages.

The tabloid New York Post reported it as 'Anti-Jewish code lurks in popular software'.

It turned out that when 'NYC' was written in Wingdings, it was rendered as a skull and crossbones, the Star of David and a thumbs up gesture. Some took this as Microsoft encouraging the killing of Jews in New York. Microsoft, understandably, denied this emphatically.

The conspiracy reappeared after September 11, when another genius discovered hidden messages in the similarly comic Webdings font that supposedly implicated Microsoft in the attacks. Watch a video about it here.

9. Nazi alien affiliation
Conspiracy theorists, who have perhaps spent too much time playing Wolfenstein, believe that Nazis landed on the moon as early as 1942.

One balanced blogger explains: "In the time just before the fall of Hitler's Third Reich, a stalwart band of scientists subverted the Luftwaffe's space program for their own purpose. In the confusion at the end of the war, these scientists escaped the bounds of Earth to establish their base on the far side of the moon. They are still there today."

Maybe that's where Hilter's assistant Martin Bormann is.

10. Facebook and the CIA
Facebook - the social networking monster that everyone's on - may have been created by secretive US government agencies hell bent on mining the personal information of millions, according to one theory.

Part of Facebook's funding supposedly came - very indirectly - from the CIA, and from the DARPA's Information Awareness Office, which had the following mission statement: "...to gather as much information as possible about everyone, in a centralised location, for easy perusal by the United States government, including (though not limited to) internet activity, credit card purchase histories, airline ticket purchases, car rentals, medical records, educational transcripts, driver's licenses, utility bills, tax returns, and any other available data."

An article about the dastardly plot has been the top-read story in nzherald.co.nz's Technology section for two years.

- NZ HERALD STAFF