One of the most famous–and controversial– psychology studies ever conducted is a fraud, a scientist claims in a new report.

Not only was the Stanford Prison Experiment a sham, but it’s mastermind, Stanford psychology professor Philip Zimbardo, pushed participants towards the results he wanted, Dr. Ben Blum claims in a report published on Medium last week.

The 1971 experiment pitted young male volunteers against each other – with some assigned to act as guards and the others as inmates in a mock prison. As the experiment began, the fake guards immediately took to their roles, instituting authoritarian measures and torturing the inmates, who passively took the abuse.

The study was supposed to last two weeks but guards were reportedly so cruel, it had to be stopped after six days.

The study made a cynical conclusion about human nature: those who are put in positions of power will naturally abuse their authority.

And people placed in situations where they are powerless, would become submissive or even crazy.

Since then, the experiment has been the subject of books, TV-show episodes, documentaries and feature films.

Blum’s expose — based on previously unpublished recordings of Zimbardo, a Stanford psychology professor, and interviews with the participants — offers evidence that the “guards” were coached to be cruel.

One of the men who acted as an inmate told Blum he enjoyed the experiment because he knew the guards couldn’t actually hurt him.

“There were no repercussions. We knew [the guards] couldn’t hurt us, they couldn’t hit us. They were white college kids just like us, so it was a very safe situation,” said Douglas Korpi, who was 22-years-old when he acted as an inmate in the study.

In a recorded clip of the experiment, Korpi was seen locked in a dark closet, naked under a thin white smock, screaming “I’m burning up inside!” and kicking furiously at the door.

But the Berkeley grad now admits the whole thing was fake.

“Anybody who is a clinician would know that I was faking,” he said. “If you listen to the tape, it’s not subtle. I’m not that good at acting. I mean, I think I do a fairly good job, but I’m more hysterical than psychotic.”

One guards told Blum he pretended to be a sadist for kicks.

“I took it as a kind of improv exercise,” Dave Eshelman said. “I believed that I was doing what the researchers wanted me to do… I’d never been to the South but I used a southern accent.”

Zimbardo has admitted that he was an active participant in the study, meaning he had influence over the results. At one point, he handed the “guards” batons, which could have implied to them that using physical force was okay. Yet, he maintained that their behaviors arose organically.

The study has long been subject to scrutiny — it was never published in a mainstream journal or subjected to peer review – but it is still widely taught in schools.

Blum’s report has spurred professors to call for the experiment to be scrapped from textbooks.

“Psychologists: please read this. We must stop celebrating this work. It’s anti-scientific. Get it out of textbooks,” tweeted UC-Davis psychology professor Simine Vazire.

“It’s also irresponsible in many other ways (socially, politically),” she added. “I’m embarrassed that my field treated this work and this man as heroic.”