Nadeen Ashraf had a burning secret. Earlier this summer, an anonymous Instagram page that named and shamed a man accused of being a notorious sexual harasser at Egypt’s most prestigious university was causing a sensation among her friends. Unknown to them, she was running it.

The experiment started, in a flash of fury, in the dead of night. On July 1 Ms. Ashraf, a 22-year-old philosophy major, was up late to cram for an exam the next morning when she became preoccupied with the fate of a Facebook post that had mysteriously disappeared.

Days earlier, a fellow student at the American University in Cairo had posted a warning on Facebook about a man she said was a sexual predator - a brash, manipulative young man from a rich family said to be harassing and blackmailing women on campus. Now, Ms. Ashraf realized as she stared at her laptop, the post had been deleted without explanation.

Enraged, she set aside her textbooks and created an Instagram page under a pseudonym - @assaultpolice - that identified the man, Ahmed Bassam Zaki, alongside his photo and a list of accusations of misdeeds against women.

“This guy had been getting away with stuff since the 10th grade,” she said. “Every time a woman opened her mouth, someone taped it shut. I wanted to stop that.”

After creating the page, Ms. Ashraf flopped into bed at 6 a.m. and slept through her exam. But when she awoke, she found hundreds of notifications from people who applauded her post, and about 30 messages from women who confided that they, too, had been assaulted by Mr. Zaki. Some said they had been raped.

An Egyptian #MeToo moment was born.

Within a week, Mr. Zaki had been arrested, the @assaultpolice account had amassed 70,000 followers and the page had prompted an outpouring of testimonies from other Egyptian women fed up with being humiliated and violated.

Sexual assault is endemic in Egypt - a United Nations study in 2013 found that 99 percent of women had experienced harassment or violence - but reporting it is notoriously difficult. Police officials are reluctant to register assault cases. Powerful institutions prefer to sweep accusations under the carpet. Even the families of victims, wary of scandal or feeling a misplaced sense of shame, tend to hush it up.

Ms. Ashraf’s bold page offered a new way.

“It was so wonderful,” she recalled, sitting in her family home. “A lot of the girls who got in touch said ‘I can’t believe I’m finally being heard.’ Even though it was a dark time, here they were speaking out. There was a sense of empowerment, of relief.”

On Sept. 1, the authorities charged Mr. Zaki, 21, with three counts of sexual assault against underage women, as well as multiple counts of blackmail and harassment. He remains in detention, awaiting trial.

But then a second high-profile case came to light, also through Ms. Ashraf’s Instagram page, that complicated matters. It promised to be even more sensational - an account of a gang rape by five young men in a five-star hotel overlooking the Nile. In recent weeks, however, the case has become clouded in a murk of counter-accusations and leaked images that threatens to overshadow the progress Ms. Ashraf has made - and possibly even reverse it.

“It’s very worrisome,” she said.

Ms. Ashraf, 22, is not an archetypal Egyptian rebel. She comes from an apolitical family that lives in a gated community in eastern Cairo - a place of manicured lawns and hushed streets lined with luxury vehicles where support for Egypt’s authoritarian leader, President Abdel Fattah el-Sisi, runs relatively high.

Her father owns a software company, her mother is a nutritionist, and her family stayed in the suburbs during the 2011 uprising that toppled Egypt’s longtime ruler, Hosni Mubarak, and the 2013 protests that ushered in a military takeover and Mr. el-Sisi’s rule.

When the #MeToo movement erupted in the United States in 2017, driven by accusations against the disgraced film producer Harvey Weinstein, she didn’t pay much attention - even if she did have her own experience of assault.

When she was 11 years old, a delivery man carrying laundry approached her as she walked down the street and slapped her bottom. “I had no idea why he was doing this,” she said. “It took me years to realize it was sexual.”

Public outrage over sexual assault has been growing in Egypt for about a decade, driven by high-profile attacks and, last year, harassment accusations against a famous soccer player. Even so, men continue to assault with impunity.

Working-class women run a gantlet of harassment in crowded public buses, Ms. Ashraf said. Among the rich, although dating is tolerated, young men exploit their family connections to misbehave with license, she said, and many parents reflexively blame their daughters when things go wrong.

“The first response is that it’s your fault,” she said. “How did he get your number? Why did you let him in?”

Ms. Ashraf initially shielded her activism from her parents, who thought she was locked into her bedroom to study. When she finally came clean to her father, weeks later, he was alarmed. “He went silent for three minutes,” she recalled. “Then he said, ‘You can’t tell anyone.’”

Ms. Ashraf told him it was a little late for that.

Is her brand of vigilantism open to abuse, or even fair? False accusations are a hazard, she admitted, adding that she tried to confirm the charges against Mr. Zaki through her network of friends. Even so, she had to delete one accusation, from his time as a business student in Spain, after it was found to be untrue.

In a country like Egypt, such methods were necessary, she said. “It’s not like the West. You can’t just walk into a police station.”

The real difficulties started, though, with the second high-profile case.

In late July, Ms. Ashraf posted to Instagram about five men in their 20s, from wealthy families, who were said to have gang-raped a teenage woman in a suite at the Fairmont Nile City hotel after a party in 2014. A video of the assault, made by a sixth man, had been distributed to their friends.

The accusation caused a sensation. Although Ms. Ashraf didn’t identify the accused men, copycat accounts sprang up on Instagram that did. One is the son of a prominent steel tycoon; another is the son of a well-known soccer coach.

Within one week the victim, who said her drink had been spiked by the assailants, approached the police and pressed charges. In late August, Egypt’s prosecutor general announced five arrests - two men in Egypt and three in Lebanon, who have since been extradited to Egypt. At least three other men are being sought.

But the investigation became muddied after investigators moved against several people who had come forward in connection to the case. Two men were accused of “debauchery” - code for homosexuality - based on photos found in their phones that were later leaked to the news media.

They have been detained, as has a woman - a former partner of one of those accused of rape - whose intimate photos have been leaked onto the internet.

Just who leaked those photos is unclear, and the cases are expected to come to court in the coming weeks. But they have already sent a chill through the ranks of Egyptian women who hoped it had become safer to report sexual violence.

“Fairmont has become our case of the century,” Ms. Ashraf said. “But it shouldn’t be a precedent for assault cases. There’s so many other things coming up that prove we are on the side of girls.”

After threats to her security, Ms. Ashraf suspended her Instagram page for 10 days in August. Now it is up and running again, but with a focus on educating women about their rights.

“You use the word consent all the time in English,” she said. “But I’ve never heard its Arabic equivalent — taraadi. So we try to translate these concepts, break them down, explain.”

The only name she’s made public of late is her own. Realizing that her identity was leaking out, and fearing retribution from men who were threatened by the page, she decided it was safest to end her anonymity. “I figured that if the bad guys knew who I was, good people should too,” she said. “There’s protection in that.”