The sprawling internet theory, beloved by Trump supporters, has ensnared everyone from Tom Hanks to Hillary Clinton

If you happened to be watching YouTube videos on Monday morning and were struck by an urge to check in on one of America’s most beloved movie stars, you were in for a nasty surprise.

“Sarah Ruth Ashcraft says Tom Hanks is a pedophile”, read the title of the top video search result for the actor’s name. “Tom Hanks’ Alleged ‘Sex Slave’ Speaks Out”, read another top search result.

Indeed, the top five results – and eight out of the top 14 – were variations on the pedophilia theme, interspersed with the hashtags #QAnon, #Pizzagate and #Pedogate.

These bizarre results, first spotted by the NBC reporter Ben Collins, are not the result of the latest #MeToo era investigation reporting. Instead, they are the entirely unsubstantiated manifestation of a sprawling rightwing conspiracy theory known as QAnon.

Here’s our best effort at explaining what you do – and don’t – need to know about QAnon.

Meet Q

On 28 October 2017, “Q” emerged from the primordial swamp of the internet on the message board 4chan. In a thread called “Calm Before the Storm”, and in subsequent posts, Q established his legend as a government insider with top security clearance who knew the truth about a secret struggle for power involving Donald Trump, the “deep state”, Robert Mueller, the Clintons, pedophile rings, and other stuff.

Imagine a mix of Pizzagate, InfoWars and the Satanic Panic of the 1980s, multiplied by the power of the internet

Since then, Q has continued to drop “breadcrumbs” on 4chan and 8chan, fostering a “QAnon” community devoted to decoding Q’s messages and understanding the real truth about, well, everything.

What do followers of QAnon believe?

It’s hard to say. The conspiracy theory is generally pro-Trump and anti-“deep state”, but it is not exactly coherent, and – like many conspiracy theories – is flexible enough to adapt to any new developments that might disprove it.

New York magazine and the Daily Beast have written articles explaining more of the basic beliefs of QAnon, but chances are that the more you read about it, the more confused you will be. Imagine a volatile mix of Pizzagate, InfoWars and the Satanic Panic of the 1980s, multiplied by the power of the internet and with an extra boost from a handful of conservative celebrities.

So celebrities believe in QAnon?

Before she was fired from her own sitcom for her racist tweet about Valerie Jarrett, Roseanne Barr raised eyebrows with a series of tweets that invoked QAnon. Barr’s tweets focused on the supposed existence of hundreds of pedophile rings, including in Hollywood, that Trump is personally breaking up.

Another high-profile QAnon is Curt Schilling, the former Major League Baseball pitcher who now hosts a podcast for Breitbart.

Does anyone else believe in QAnon?

Yes, but it’s not clear how popular it actually is. Joseph Uscinski, a University of Miami professor who studies conspiracy theories, said by phone that QAnon remains a “fringe” belief held by “a very small number of people”. “Don’t confuse the popularity of this with the popularity of Kennedy assassination theories,” he said.

Most QAnon followers are Trump supporting evangelicals, Uscinski said, who are predisposed to believe a pro-Trump, anti-liberal narrative. Uscinski also cautioned against treating QAnon followers as any more gullible than other people.

Facebook Twitter Pinterest Roseanne Barr has raised eyebrows with tweets that evoked QAnon. Photograph: Julie Jacobson/AP

“People believe all sorts of crazy stuff,” he said. “We shouldn’t come at this from the standpoint that most people believe sane stuff and this is just crazy. Like all conspiracy theories, this has a foot in reality.”

The idea that the “deep state” is working to take down Trump might be far-fetched, he said, but chances are there were many government bureaucrats who did not welcome his presidency. As for accusing beloved stars like Hanks of being pedophiles:

“Bill Cosby was America’s dad,” Uscinski pointed out. “Now it turns out he’s a serial rapist. So how much should we be blaming people for thinking ‘Hey, maybe there’s something beneath the surface?’”

Does any of this really matter?

Sort of. Not because it’s true, but because people who believe it’s true might act on that belief.

People respond very strongly to the threat of sexual violence against children. In 2016, a Washington DC pizza restaurant became collateral damage in the #Pizzagate conspiracy theory. The fear of satanic sex abuse rings in the late 1980s led to many criminal convictions, with some of the accused only being exonerated after serving years in prison.

Indeed, there have already been some incidents where QAnon followers have taken their search for pedophiles into the real world.

“We need to be really careful, because we have a history of witch-hunts,” said Uscinski.

Can we get back to the part about YouTube?

Sure. Here’s the part about YouTube.

'Fiction is outperforming reality': how YouTube's algorithm distorts truth Read more

For years now, YouTube has been a quagmire of conspiracy theories, the more outrageous and thinly sourced the better. Under pressure from the mainstream media for the platform’s tendency to promote inflammatory and false information in the aftermath of mass shootings and other breaking news events, YouTube has introduced reforms that it claims will promote more “authoritative” news sources.

A YouTube spokesperson provided a statement that did not directly address the Guardian’s questions about the Hanks videos, but noted that the company’s work to “better surface and promote news and authoritative sources” is “still in its early stages”.

By Monday afternoon, hours after the Guardian first queried YouTube, the search results for “Tom Hanks” had reverted to videos of the actor’s appearances on various talk shows. Search for “Tom Hanks pedophile”, however, and you’re back in the world of QAnon.