Well-known right-wing personalities and fringe websites are pushing conspiracy theories on social media platforms about the mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida.

At one point on Wednesday morning, the top trending video on YouTube was one suggesting that student David Hogg, a survivor of the Feb. 14 shooting who's appeared on cable news, was an actor following a script, perhaps written by his father, a former FBI agent. Since the shooting, 17-year-old Hogg has become an outspoken advocate of gun control.

YouTube later removed the video, but a number of other similar videos remain available to watch on the site. It’s similar to what happened on social media platforms after the shootings in Las Vegas last October and at Sandy Hook Elementary School in 2012.

“This video should never have appeared in Trending. Because the video contained footage from an authoritative news source, our system misclassified it,” a YouTube spokesperson said in a statement emailed to VICE News. “As soon as we became aware of the video, we removed it from Trending and from YouTube for violating our policies. We are working to improve our systems moving forward.”

YouTube monitors and curates trending videos entirely using an algorithm, because the company claims that the sheer volume of videos being scanned makes it impossible for humans to do the task. The algorithm weighs authoritative sources — like a local Florida affiliate of CBS, in this case — differently than some of the lesser-known or even unheard-of sites also spreading the theories, like DCWhispers.com or 153news.net.

The conspiracy theory about Hogg also made the rounds on Facebook. A search for “David Hogg” or “crisis actor” surfaced a wide variety of similar videos and posts. They claim Hogg and other survivors speaking out about politicians’ failure to pass gun control laws are being paid or acting on some sort of illegitimate basis. Among the claims is one saying left-leaning billionaire George Soros has paid some of the students to speak out, or that they’re acting out someone else’s hidden agenda by reading from a script.

Facebook is now targeting such posts. “Images that attack the victims of last week’s tragedy in Florida are abhorrent. We are removing this content from Facebook,” said Mary deBree, head of content policy, in an email to VICE News.

While a significant chunk of these conspiracy theories come from fringe sites, more well-known right-wing figures like Alex Jones and Infowars are openly speculating about the authenticity of the Stoneman Douglas shooting survivors’ media appearances. On Twitter, former Milwaukee County Sheriff David Clarke, who was reportedly offered a position as a senior official in Trump's Department of Homeland Security, claimed that Soros is likely behind the students’ activism.

Donald Trump Jr. also clicked “like” Tuesday morning on two tweets advancing the conspiracy theory that Hogg was “running cover for his dad,” a retired FBI agent. The agency admitted that it had failed to follow protocol and follow up on a report about the 19-year-old who terrorized Stoneman Douglas.

For their part, Hogg and the other Stoneman Douglas students don’t appear to be backing down in the slightest.

“I’m not a crisis actor. I’m somebody who had to witness this and live through this, and I continue to have to do that,” Hogg told CNN on Wednesday morning.