PARIS (AFP) - The QAnon conspiracy theory has been blamed for fuelling a riot at the US Capitol on Jan 6. Social media companies have begun to crack down on its followers, with Twitter closing 70,000 accounts on Monday.

AFP explains the origins and beliefs of what was once a fringe internet phenomenon:

How did it start?

In 2016, a false theory spread on the Internet, which eventually became known as "Pizzagate," alleging that top Democrats ran a child sex-trafficking ring from a pizzeria in Washington DC.

It appeared to have been sparked by innocuous messages published by WikiLeaks recounting a Hillary Clinton fund-raiser, and culminated in a man firing a gun in the restaurant in December 2016.

QAnon began in late 2017 with posts on the anonymous messaging board 4chan and a similar site, 8kun, by a user named "Q Clearance Patriot," who claimed to be an American intelligence official with access to classified information.

Q alleged that Democrats ran a Satanic child-kidnapping and paedophile ring and that the US security establishment, referred to as the "deep state," was conspiring to cover it up along with a global liberal elite.

According to the story, US President Donald Trump was working against them and a "great awakening" could be expected.

Q moved his or her posts to more prominent sites and picked up followers, helped by Trump's repeated claims that there was indeed a plot against him from inside the US government.

Followers began to identify themselves with shirts and patches with large "Q" symbols, often together with the US flag and their motto "Where We Go One, We Go All," expressed #WWG1WGA.

How did it go mainstream?

Fuelled by sharing on social media, the movement gathered momentum, picking up thousands then hundreds of thousands of followers in a loose network.

Researchers say the movement drew in white supremacists and other far-right followers, as well as so-called "anti-vaxxers" - people who believe in conspiracy theories about vaccines.

The Covid-19 pandemic appears to have been a major catalyst, with researchers saying there is an overlap between protesters against mask-wearing and social distancing and QAnon believers.

The QAnon movement is a "sponge for conspiracy theories. Everything is taken seriously, from anti-Semitism to 5G to masks, including science fiction," said internet researcher and academic Tristan Mendes France from the University of Paris.

Miro Dittrich, a German researcher who monitors online extremism, said conspiracy theories tended to flourish in times of crisis, when people feel they have no control or are looking for scapegoats.

"As after Sept 11, which inspired many conspiracy theories, I fear we are witnessing the same phenomenon with the pandemic," Dittrich told AFP recently.

In Europe, where QAnon has gathered tens of thousands of followers, strict lockdowns have also helped garner interest, according to Dittrich.

"Confinement has played a role, with people being isolated from their social environment and spending a lot of time online," he said.

Research by the London-based ISD think tank found that QAnon-related posts on Facebook nearly tripled between March and June last year, when stay-at-home orders were in place around the world.

Does Trump support QAnon?

Trump has never condemned the movement and fed QAnon fever before last November's US presidential election, floating his own conspiracy theories about a planeload of black-clad saboteurs disrupting his party convention.

"It is gaining in popularity," he said approvingly in August last year. "They like me very much."

Rich Hanley, a professor at Quinnipiac University's School of Communications in Connecticut, told AFP that Trump reflects - and profits from - a society ever more lost in the smoke and mirrors of the Internet.

"He may be an outlier among presidents, but not among a growing number of conspiracy theory-loving Americans," Hanley told AFP in September.

Trump has also lavished praise on Marjorie Taylor Greene, one of several QAnon followers elected to the US Congress last November.

Greene, who has said that "Q is a patriot," said she was "inspired" to run for office by Trump.

What is being done about it ?

Following the riot at the Capitol, criticism of Facebook and other social media platforms including Twitter and Parler reached fever pitch over their role in spreading disinformation.

"You've got blood on your hands, @jack and Zuck," tweeted Chris Sacca, an early Facebook investor who has become one of the network's harshest critics, referring as well to Twitter's chief Jack Dorsey.

As well as suspending Trump's account, Facebook says it is now taking action by deleting QAnon accounts and investing more in its fact-checking operations.

Twitter announced Monday that it had suspended more than 70,000 accounts linked to the QAnon theory.

Both platforms have warned about the risk of future violence, particularly before US president-elect Joe Biden's inauguration on Jan 20.

Meanwhile Parler, a conservative social network that functions without moderators and is favoured by Trump allies and supporters, was forced offline on Monday when Amazon's web unit cut access to its servers.

Mendes France said the crackdown on mainstream platforms risked driving believers towards fringe internet sites.

"The problem is that the move to more radical platforms exposes the 'soft fringe' of the movement to even greater radicalisation," he said.