David Hogg, 17, went from Florida high school student to mass shooting survivor to telegenic advocate for gun control laws in a few days. And just as quickly, online conspiracy theorists began spinning viral lies attacking the teenager’s credibility.

By Wednesday — a week after a gunman wielding a semi-automatic rifle killed 17 people at Hogg’s Parkland, Fla., school — online media sites including YouTube swelled with false allegations that Hogg was secretly a “crisis actor” playing the part of a grieving student in local and national television news reports.

Hogg was not alone in being targeted by an online campaign that flared up on anonymous forums such as 4 Chan and Reddit before reaching conservative websites, Twitter, Facebook and Google’s video platform. Collectively the posts questioned the honesty and credibility of the grieving students as they spoke out against gun violence and in some cases publicly challenged President Donald Trump, the National Rifle Association and lawmakers opposed to gun control.

“It’s annoying. I hate it. But it’s part of American democracy,” Hogg said in a phone interview. “Am I an actor? No. Am I a witness? Yes.”

The falsehoods about Parkland students come even after the technology giants have tried to tamp down on disinformation campaigns by hiring thousands of moderators, changing the algorithms that surface information and enacting stricter policies. The Parkland flare-up underscores how efforts to quell the spread of such online conspiracies remain incomplete on platforms that derive profits by attracting eyeballs en masse.

The incident has also highlighted how nobody — even a group of teens just days removed from seeing their fellow students gunned down — is off limits in the no-holds-barred world of online commentary, with its often-toxic mix of rumor, innuendo and unrefuted accusation.

The president’s son, Donald Trump Jr., was among the many people who “liked” a tweet criticizing Hogg. On YouTube, a video featuring one conspiracy theory reached the top of its “Trending” clips list and was viewed more than 200,000 times before the company admitted its filtering of news had not functioned as intended, and it blocked the video. A search for Hogg’s name on YouTube on Wednesday turned up eight conspiracy videos and only two legitimate news reports in a top-10 listing before YouTube intervened.

The conspiracy theories about Hogg grew from a combination of facts and falsehoods, mixed together with authentic photos and videos collected online, making it more difficult for the algorithms on social media platforms to detect false information.

Mike Cernovich, a far-right social media commentator who sometimes appears on the Infowars conspiracy site, said it’s possible to concoct a video in as little as 20 minutes that splices together images and text to create an alternative narrative capable of spreading rapidly on social media.

Postings skeptical of the news reports about the Parkland shooting began appearing on 4 Chan just hours after the rampage.

Online talk of a “false flag” attack — essentially a fake in which the real culprit is trying to frame somebody else — started soon after the Parkland survivors started speaking on television and social media about the horror of the shooting and demanding government action to prevent yet another one.

Hogg became the target of some of the conspiracy stories after he mentioned in one interview that his father was a retired FBI agent, allowing the online narrative to merge with ongoing attacks against the bureau. The FBI has been under fire from conservatives over its investigation into allegations that the Trump campaign colluded with the Russians during the 2016 presidential campaign, and President Donald Trump has blamed the Parkland shooting on the FBI’s failure to follow up on a tip about the suspect.

The conservative website Gateway Pundit on Monday posted a picture of Hogg under the headline: “EXPOSED: School Shooting Survivor Turned Activist David Hogg’s Father in FBI, Appears To Have Been Coached On Anti-Trump Lines.”

Hogg’s mother, Rebecca Boldrick, an elementary school teacher, scoffed at the conspiracy theories growing online about her son and other Parkland students. She said her husband, a Republican, worked for the FBI as an agent at airports in Los Angeles and Florida before retiring from the bureau in October 2016.

About the same time as the FBI stories popped up, posts emerged alleging that the Parkland students were “crisis actors.”

Such allegations are a mainstay of conspiracy reports about mass shootings, with some gun-rights activists claiming that those favoring stricter gun laws hire actors to pretend to be victims of phony attacks.

“You have the same three or four tropes that get floated again and again,” said Whitney Phillips, a Mercer University professor who studies the relationship between online trolling and mainstream culture. “It’s hard to know what is causing it. But as a person who has been studying this a lot, I brace myself for the narrative that I know is about to unfold” each time a shooting occurs. In October, YouTube said it would change its algorithm to elevate authoritative news sources after hoaxes quickly dominated the site after the Las Vegas shooting.

Google, which owns YouTube, said in a statement Wednesday that it had removed several videos related to Hogg for violating company policy on harassment. “We recognize the challenging issues presented by hoax videos and the pain they can cause the families who have suffered these incredibly tragic losses.”

The recommendation engine on YouTube, which has 1.5 billion monthly users, features a list of links that play automatically when a person clicks on them. Such recommendations are the way thatmost YouTube users find and discover content.

Guillaume Chaslot, a former YouTube engineer who worked on the recommendation algorithm, says YouTube recommends conspiracy theories with abnormal frequency, in part because its algorithm favors links that encourage people to watch longer.

“People who distrust other media tend to spend more time on YouTube,” he said. “Since the algorithm is optimizing for watch-time, it figures that recommending conspiracy theories is efficient.”

A post on Facebook featuring a photo of Hogg and claiming that the Parkland students were actors also was shared more than 100,000 times before Facebook later deleted it for violating its policies. “Images that attack the victims of last week’s tragedy in Florida are abhorrent,” said Mary deBree, head of content policy for Facebook.

Conspiracy theories around “crisis actors” — feigning grief and working to build support for tougher gun laws — start with a premise that the event never occurred, according to Kate Starbird, a University of Washington professor who runs a lab that tracks the spread of online rumors after disasters.

Starbird said her lab has documented both domestic sites and some tied to foreign governments in Russia and Iran amplifying the narratives, including after the Pulse nightclub shooting in Orlando.

“The goal seems to be to want to undermine the collective response to tragedy,” she said. They hark back to “a high-level narrative, which is the media is lying … and you can’t trust anything you see.”