Supporters have rallied round the actor Emma Watson after a threat emerged online to release nude photos of her in response to a speech about gender equality she made at the United Nations over the weekend.

Watson, the newly appointed UN Women’s goodwill ambassador, spoke on Saturday about her journey to call herself a feminist in a speech to launch the HeForShe campaign, a solidarity movement that seeks to have men and women work together for gender equality.

“I want men to take up this mantle,” Watson said. “So their daughters, sisters and mothers can be free from prejudice but also so that their sons have permission to be vulnerable and human too – reclaim those parts of themselves they abandoned, and in doing so be a more true and complete version of themselves.”

In response, users on the anarchic message board 4chan, where leaked celebrity photographs first appeared last month, posted a link to “emmayouarenext.com” with a picture of Watson and a countdown, which ends just after midnight ET on Friday night. A caption at the bottom of the screen says “never forget, the biggest to come so far”. Users also posted fake reports of Watson’s death on Twitter.

The weight of that threat is in question for a number of reasons, including that none of the other recent leaks have been trailed in this style. “If anyone from 4chan had the skill to do this,” one anonymous poster said, “there’d be no threats, only nudes.”

On 4chan, it is near impossible to tell what is real and what is “trolling” – misdirection and mischief. The Watson threat bears all the hallmarks of the latter, and the general consensus among commenters is that this is a prank. “Spoiler: it’s not true,” one anonymous 4chan poster said.

Either way, feminists are railing against the threat against Watson. “Emma Watson, like so many other women online, is being silenced and kept in her place with misogyny as a weapon,” said PolicyMic senior editor Elizabeth Plank.

“So go ahead and add this response to Watson’s argument for why we need feminism,” wrote Maya Dusenbery, executive director of Feministing. “Misogynists do have a tendency of proving your point for you – they can be helpful like that.”

Watson, surely aware of the threat, is still posting support for the campaign on Twitter.

Her speech, and the HeForShe campaign, have received support from celebrities including comedian Simon Pegg, author Neil Gaiman and actor Joseph Gordon-Levitt, who is working on a film project asking people to define what feminism means to them.

Commenters on Reddit concurred that the threat of a leak is likely a hoax. “This is a masterwork of trolling,” said a user with the handle JS945. A popular theory is that this is an elaborate version of a classic internet prank known as “Rickrolling,” in which people are tricked into clicking a link that leads to a video of ‘80s star Rick Astley’s Never Gonna Give You Up.

“Mark my words. Rickroll,” said one Redditor whose username was Forceblade. “The biggest Rickroll in internet history” another agreed.

A few 4chan users had a different theory: that this was an elaborate “false flag” by the government to turn public opinion against internet freedom. “These leaks are definitely false flags targeting 4chan,” said one user. “Guys, guys, guys. Listen guys,” said another. “What if the hacker was NSA? What if the NSA did this to sway the public for censoring the internet? You think they would do something like that?”

“All I can say Emma, is: fuck them,” wrote Rhiannon Lucy Cosslett in a letter to Emma Watson posted in the New Statesman. “It makes me furious that these men, these boys, are attempting to grind you down, in the same way that similar men have tirelessly attempted to grind down the emergence of our gender as a viable political threat for generations now.”

• This article was updated on 24 September to make it clear that the original threat against Watson did not originate on 4chan. While users there shared the link to the threat, its source is currently unclear.