Soraya Bahgat, a Cairo-based HR executive and postgraduate student, was on her way to join Tahrir Square protests on November 25 when an unwelcome thought stopped her in her tracks.
Mobs in the square had sexually assaulted women protesters there a week earlier, and reports of such incidents had become common enough for her to fear a repeat occurrence.
"A panic attack gripped me and prevented me from going because I thought no woman should go through this," said the 29-year-old.
"It was almost two years since the Lara Logan incident," she said, referring to the harrowing sexual attack on the CBS correspondent by a mob in Tahrir Square.
"I didn't understand what else we needed before collective action was taken to prevent these assaults. I felt that it was time to step up and do something about it."
Instead of going to Tahrir -- where, according to local reports, three women were sexually assaulted among the crowds that day -- she took to Twitter and started an account, Tahrir Bodyguard, encouraging a "collective effort to promote the safety of women protesters."
The response, she said, was "overwhelming."
Today Tahrir Bodyguard has a database of 200 volunteers, who patrol the square during mass demonstrations, recognizable in high-visibility helmets and vests, intervening to halt the attacks on women that have blighted Egypt's revolution and its aftermath.
In a recent mass demonstration on January 25, for example, 25 sexual assaults were reported on women in the square. Tahrir Bodyguard intervened to rescue the victims of 10 attacks.
While the group consisted of men and women, Bahgat said it was generally men who intervened when an assault was detected, to prevent women bodyguards from being sexually assaulted themselves.
The group also organizes free self-defense classes for women.
Bahgat described Tahrir Bodyguard as "a story of what an individual with a computer and a Twitter account can start," said Bahgat. "It gives me faith when I see these young boys and knowing they're going to be potentially hurt to protect a woman and save her from sexual assault."
One of the men involved in the group is 27-year-old petroleum company employee Mark Beshara, who has patrolled Tahrir on seven occasions, intervening to stop 15 assaults and being injured in the process.
He became involved in the group after being haunted by the memory of witnessing men in the crowd assaulting a woman in the square in November.
"It was very noisy and about 50 or 60 people were surrounding something. At first I thought they were catching a thief or there was a fight," he told CNN. "Then someone told me 'There's a poor girl in there'."
The size of the crowd made it impossible to intervene alone, he said. "On my own I can't help at all. If I was in a team I would be able to help her."
When he heard of Tahrir Bodyguard, he didn't hesitate to become involved. The group has quickly learned what works in breaking up the assaults, he said.
When trying to help a woman escape, he said, "the most important thing is you have to get her trust."
"She's in a hysterical state, standing there in cut clothes, and being harmed. First you have to tell her several times your name and that you're there to protect her."
Recounting a recent intervention by his group, he said the woman was too traumatized and disoriented by what was occurring to register the group's presence.
"I looked her in the eyes and said 'I'm your only chance to get out of this crowd.' Then I turned around and gave her my back to climb on to. When I felt her hands were catching, I told the crew, 'Let's move.'"
Sexual harassment is a longstanding problem in Egypt, said Bahgat.
According to a 2008 survey of 1,010 women conducted by the Egyptian Center for Women's rights, 83% of Egyptian women and 98% of foreign women there have been sexually harassed.
Activists have developed a system to track and map incidents of harassment through mobile phones, in an effort to challenge the social acceptability of harassment.
But Bahgat said the mob assaults of women that had been occurring during protests since the revolution, some of which have reportedly included bladed weapons, were something "entirely new."