HARI SREENIVASAN: Now to Egypt.

Among the demonstrators who jam Tahrir Square every day are hundreds of women. They face a very disturbing threat from gangs of men who sexually assault female protesters.

Lindsey Hilsum of Independent Television News reports from Cairo.

And a warning: You may find some of the details and the images in her story distressing.

LINDSEY HILSUM: Such sweet boys full of energy and fun. They have just been chasing a young woman up the street. The interviewer asks them why.

"If a lady is respectable, no one will harass her," says a kid in red. The others pile in. "Why do they wear short skirts or tight trousers?"

"Some young women, when we flirt with them, they smile."

That's how it starts. This is how it ends. A mob attacks a young woman on the corner of Tahrir Square. We have disguised her identity.

This is one of more than a hundred assaults in Tahrir Square during last week's demonstrations. This is the very place. Women still come to the square, but it's dangerous.

This corner of Tahrir Square has become notorious for attacks on women. I can only come here tonight because it's almost empty because of Ramadan and people are praying. And I have got a whistle to protect me and an alarm and a whole crew of people around me. That's not the case for many women who come here.

And the most horrific thing I have heard is that these attacks are planned, and, sometimes, women think that the men coming for them are trying to save them from being assaulted, but in fact they take them away and attack them again.

A long darning needle. Janet Abdel Aleem and her group of activists distribute the needles to women for self-defense. She and her colleague Nada were assaulted in Tahrir Square last November.

JANET ABDEL ALEEM, Fouada Watch (through translator): They were putting their hands into my pants and into Nada's pants and inside my blouse, touching me everywhere. There were about 15 to 20 people who said they were trying to protect and save us, but they suddenly started to attack us.

LINDSEY HILSUM: Today, the Muslim Brotherhood are on the streets. The women tell me it's the secularists in Tahrir Square, not religious men, who do it.

WOMAN: No, that's in Tahrir Square, not here; 170 women get raped in Tahrir Square, because I don't know which kind of people is going to Tahrir Square. Maybe it's the people, they freed them when they open prisons.

LINDSEY HILSUM: But both political factions have tried to intimidate women off the streets at different times. And the Muslim Brotherhood blocked a law on violence against women.

Law and order collapsed under their rule, so voluntary groups had to step in.

ZEINAB SABAT, Tahrir bodyguard: We're doing the job of the police. We're doing the job of people who are in power who should be responsible for this.

LINDSEY HILSUM: Zeinab is planning to join her male colleagues intervening to save women being attacked in Tahrir Square, because the victims now fear that rescuers may in fact turn out to be rapists.

ZEINAB SABAT: I reached the point where I don't get scared anymore. Now when someone touches me when I'm trying to, not intervene, but patrolling at least, or anything like that, it's never fine. But kind -- I know it's part of the job, like, it's something that you cannot prevent for now.

But when it comes to intervening, I saw cases. I saw victims and I -- it's traumatizing, and I see them. And I feel that it's not -- you cannot trust a man anymore.

LINDSEY HILSUM: Poverty, unemployment, segregation of the sexes, many factors contribute to endemic sexual harassment in Egypt. But deprivation in social attitudes are not the only causes.

JANET ABDEL ALEEM (through translator): The problem is, there's no law against this. People know if they go into the square and touch women, they will not be punished. Also, us women are blamed for being harassed. We shouldn't blame women for this.

LINDSEY HILSUM: In Tahrir Square, they're holding Ramadan prayers just next to the place where women are frequently raped. Mob assaults and escalation of sexual harassment are the unintended consequence of a revolution that was meant to liberate Egyptians, men and women alike.

RAY SUAREZ: The Muslim Brotherhood and other groups are calling for a million man demonstration tomorrow in Cairo. Its aim is to protest President Morsi's ouster and clashes with Egypt's military that left more than 50 people dead.