The alt-right framed student protesters as pedophiles on Monday night. Within 90 minutes, even Donald Trump Jr. had bought into the hoax.

Mike Cernovich, an alt-right conspiracy theorist, was at Columbia University Monday night to give a speech to the school’s College Republicans club. But when students protested outside the event, trolls posed in front of them with a banner promoting NABLA: the North American Man-Boy Love Association. Cernovich and other alt-right figures quickly copied a journalist’s picture of the sign and tweeted it as evidence that the anti-Cernovich protesters were pro-pedophile.

The demonstration, organized by Columbia students, was in protest of Cernovich and other far-right speakers at the school

“This goes beyond what college Republicans are planning in terms of speakers,” student Jasmeen Nijjar who helped organize the protests told The Daily Beast. “It’s also about Columbia being in the Harlem community, and how pervasive the idea of white supremacy is, and how complicit Columbia is to allow such speakers on campus.”

Writer Jake Offenhartz was covering the protests for the New York City blog Gothamist when at least one masked man moved to the front of the crowd with a large banner that read:

“No white supremacy, no pedo bashing, no Mike Cernovich,” over a slew of logos including one that read “New York City Antifa” and another that read “NAMBLA.”

At least two people at the Columbia event “unveiled the banner and handed it to a couple of people who held it without really of looking at it,” before disappearing into the crowd Offenhartz told The Daily Beast.

“ But 30 minutes after Offenhartz tweeted the picture, Cernovich copied it and posted it without context or credit. ”

Mistee Denson, a Columbia graduate student who organized the protests said the protest had approximately 250 attendees, many of whom students did not recognize.

“There were a lot of faces we didn’t recognize, and a lot of people with their own signs with their own opinions,” Denson told The Daily Beast. “We were behind the sign and didn’t know what it said. Somebody said ‘hey can you hold this for a second?’ They were disguised as antifa.”

But protesters were quick to pick up on the ploy.

“People involved with these protests are very cognizant about plants, so they realized very quickly what was happening,” Offenhartz said. “It was up for about 10 seconds before a couple protesters ran over, explained what was happening, and threw it to the ground and ripped it up.”

Offenhartz took a picture of the NAMBLA sign and tweeted it, noting that it was the product of trolls who sometimes plague protests. “Alt right strikes first at Columbia Cernovich event, plants NAMBLA-branded sign in front of protest march,” he wrote.

Inside at Cernovich’s speech, the alt-righter also accused protesters of supporting pedophiles. “He kept saying ‘you support pedophilia,’ repeatedly,” Denson said. “He kept saying ‘you just love pedophilia’ over and over again.”

30 minutes after Offenhartz tweeted the picture, Cernovich copied it and posted it without context or credit. “NAMBLA sign at Columbia protests,” Cernovich tweeted, “these people are sick.”

Other alt-right personalities like Jack Posobiec and Watson quickly followed suit, with Watson writing an InfoWars post “Antifa Activists Carry Pro-Pedophile Sign At Cernovich Protest.”

And in under two hours, Donald Trump Jr. was buying into the conspiracy theory. The president’s son liked Cernovich’s tweet calling protestors “sick,” as well as two tweets from Watson that claimed “antifa and social justice warriors” were allying with pedophiles, and that the picture was “coffin nails to the left.”

Nevermind that actual leftist protesters had ripped up the sign within seconds, or that the rest of Offenhartz’s pictures revealed that the banner had been removed.

Alt-righters sometimes pose as leftists in an effort to discredit them. Right-wing tweeter Jack Posobiec has previously planted a “Rape Melania” sign to incriminate leftist protestors, and posed as a representative of the Women’s March at a pro-net neutrality rally where he distributed flyers claiming to thank net neutrality advocates for “protecting our quality violent porn content,” including “ritual Satanic porn videos.”

As for NAMBLA, it’s more or less dead, a 2016 Vice investigation found. The organization reportedly boasts almost no members, let alone a coalition of protesters who would choose to demonstrate against Cernovich, who was charged with rape in 2003 (it was downgraded to misdemeanor battery). Cernovich has also made statements dismissing date rape, such as, “Have you guys ever tried ‘raping’ a girl without using force?” he tweeted in 2012. “Try it. It's basically impossible. Date rape does not exist.” He later told The Daily Beast that he had been discussing rape fantasies, and that the tweet was appropriate in context.

The New York City Antifa, whose logo appeared on the sign, also debunked the image. “Cernovich trolls come to antifascist side with absurd and offensive sign,” the group tweeted. “Reportedly got chased off immediately.” The group later pointed out that the sign had printed their logo wrong, with a red flag instead of black.

Offenhartz, who was still covering the protest, didn’t realize for several hours that alt-righters had reappropriated his picture, which he had taken in his capacity as journalist. He reported some of the images to Twitter for copyright infringement. But Watson hit back, writing that Twitter was “trying to censor this image.”

Trump Jr. liked that tweet, too.

“It’s kind of hard to tell who believes this and who’s being glib, just trying to give antifa and protesters a bad name,” Offenhartz said. “It’s hard to know: does the president’s son believe Twitter is censoring photos that connect protesters to a pro-pedophile cause? Maybe. It’s not much crazier than other things he’s tweeted or liked. I wasn’t really that surprised.”