The video title reads: The result of a non-frigid 14-year-old. Gemma* appears to the sound of a frenzied drum and bass soundtrack. Fully dressed, she begins to strip and, for the remainder of the four-and-a-half minute production, masturbates for the viewer. It is believed she took the video herself using a webcam, adding the title and music later.
I haven't seen it. Doing so would be illegal. But I am reliably informed by a group of Year 11 pupils at South Dartmoor Community College in Devon that this was what they saw when the video was sent to pupils' mobile phones early last year. Everyone at their school has seen it, they say.
"We've all seen the video. She was a pupil at another school, but it was sent to people at our school using Bluetooth," says the group.
They know little about the girl, not even her name. But it is apparently common knowledge that she took the video for her boyfriend. When they broke up soon after, he sent it to some friends. And on it went. "It's pretty common," they continue. "Videos, pictures, often of things that happen at parties. Pictures get sent to boyfriends and that kind of thing."
And it isn't just the naughty kids who are doing it. It is often the ones you would least expect, they tell me. Why are so many doing it, do they think? "Kids are desensitised from a young age. And they're not properly educated on the subject, so they end up thinking it's appropriate to do what they see on websites and in magazines. Some girls think their boyfriends will be impressed with them if they do it. Some boys threaten to break up with them if they don't. Younger girls see older girls doing it as role models. They also sometimes see glamour models as role models."
John Carr, secretary for the Children's Charities' Coalition on Internet Safety, agrees that the practice is far from unusual. "There's no doubt that kids downloading, sharing and even creating their own images and videos is a big and growing problem. But we've suddenly become aware that kids are taking completely inappropriate pictures of themselves and sharing them on their phones, social networking sites and YouTube."
It is believed that the police have been involved in about 90 such cases across the country. Mr Carr adds: "There's hardly a secondary school in Britain where this isn't an issue now. I know there is a lot going on at independent boarding schools where kids live for five or six days a week and often have state-of-the-art phones."
A spokeswoman for the Child Exploitation and Online Protection Centre - the arm of the police dedicated to protecting children from sexual abuse - confirmed that the organisation has detected a huge increase in self- generated images and the problems associated with them being used against young people.
But the people involved in creating their own images are not the only ones who suffer. Ethel Quayle, a lecturer at the University of Edinburgh who has written on the subject, notes a similar case to the one above. But in her example, the wrong girl was accused of featuring in the video, "with quite distressing consequences for her". The police were involved and eventually the correct girl was identified. Neither was prosecuted.
Children caught in the United States aren't quite so lucky. Mr Carr notes: "In the US, hardly a day goes by without a report that police have prosecuted a child for this, which really isn't helpful."
But why are they doing it? Children are big consumers of porn. The Sex Education Show vs Pornography, a TV programme shown on Channel 4 in March, surveyed more than 400 pupils, aged 14 to 17, in four schools in the south and west of England. The average teenager, the survey suggested, claims to watch 90 minutes of porn a week. This includes anything from straightforward intercourse to group sex and bestiality. A third said they learnt about sex from porn.
Teacher and behaviour expert Tom Bennett hasn't encountered the self- generated variety, but he acknowledges that young people are viewing some shocking material. "I've caught plenty of boys with nudies on their phones and stood by as they deleted them. I hear many hair-curling stories and issues even worse than video texts of someone's gonads. Kids can access a diet of hardcore as soon as their parents' backs are turned. And it's not simply a question of the depth of the hardcore, it's the breadth too; not a human peccadillo or fetish is unavailable to them. My pupils have discussed extremities of human desire so loosely connected to the sexual act itself that it scarcely can be described as such."
Although studies such as the Byron Review into internet safety - commissioned by the Government and published last year - provide no evidence of any causal relationship between online pornography and young people's behaviour or attitudes, many believe there is a link.
Dr Michele Elliott, founder and director of Kidscape, is one of them. "There's no research that I know of that proves viewing porn can lead to sexually deviant or harmful behaviour, but it's common sense. We've had kids who have had porn sites made up about them. The problem is that kids will often not understand that what they're doing is pornographic. They might think it's cute or funny."
Sandrine Leveque, campaigns manager for lobby group Object, agrees. "We would definitely draw a link. Some newspapers include pages for male readers to post sexually explicit photos and videos of their ex- girlfriends and this is replicated in lads' mags, which urge readers to send in porn images of their girlfriends and encourage them to spy on good-looking women. In this context, it is unsurprising that young people in schools compete to show their `sexy' credentials and use mobile technology to do so."
For Mr Carr, exposure to porn creates a pressure on pupils to perform: "If you want to be hip and cool, you have to do it."
Donald Findlater, director of research and development at child protection charity The Lucy Faithfull Foundation, acknowledges that research is inconclusive, but says there is a clear message in most that he has seen - the younger people view sexually explicit material, the younger they'll try out the behaviour.
As most pornography tends to depict unprotected sex outside of relationships and devoid of affection, this is a troubling prospect. Mr Findlater adds: "Some material is utterly sadistic and brutish. Often children and young people are viewing this in the absence of mitigating conversations or teaching from parents or schools that can impart or convey any moral, relational, respectful aspect to sexual behaviour."
DIY porn is not the only potential negative product of kids being exposed to such a variety of material on such a frequent basis. Even more harmful behaviour can also be attributed to it. Recent Government figures show that in 2006-07 there were 3,500 fixed period exclusions and 140 expulsions from schools in England for sexual misconduct, which covers anything from explicit graffiti to serious sexual assault and rape. About 260 of the pupils were still at primary school.
Although Mr Bennett thinks the link between porn and sexual misbehaviour is tenuous, he admits it exists. "Years ago, I dealt with the behaviour of three pupils who were sexually assaulting a classmate. They genuinely thought it was just a giggle, much like holding someone down and tickling them. Of course, to the young girl it was a vicious and traumatic attack. It took a lot of talking to get them to accept that they had acted in a way profoundly out of sync with the expectations of society, and deeply wrong. Since then, I have caught these boys with a variety of easily accessible pornography."
Saying there is a causal link is too easy and empirically impossible to verify, he says. "But there was clearly an attitude in common, the perspective that intimate physical contact is meaningless, trivial and requires no consent."
He adds: "I've heard boys say that a girl isn't really your girl until she's had anal sex with you, and comments of that nature."
According to Mr Findlater, sexual bullying is becoming increasingly commonplace. The NASUWT teachers' union has talked publicly about cases where female teachers have had pupils make sexual remarks to them, use their mobile phones to photograph their cleavage, post comments of a sexually explicit nature on the internet and, on rare occasions, threaten them with sexual assault.
Chris Keates, the union's general secretary, said earlier this year: "There is evidence from our members that female pupils face the same appalling behaviour. That there is a problem is undeniable."
But many schools are unaware of the extent of the problem because of the failure to collect data, and there is evidence that too many schools are not taking this form of bullying staff and pupils seriously, she said.
Whether downloading and viewing, performing and publishing or bullying with porn, teachers are often oblivious to what their pupils are getting up to, both in and out of school. Firewalls tend to prevent downloading on school computers. But teachers will inevitably find it difficult to detect pupils sharing images and videos outside school and via mobile phones.
Ray Tarleton, principal at South Dartmoor Community College, says: "We don't always pick up on what they're doing. We think it's happening - downloading porn outside school - but don't know about it. The only way to really find out would be to do a survey. If we were to do a national survey, I think we'd be horrified."
So what can be done about the wider problem? For Mr Findlater, schools and parents need to collaborate more. "Parents need a big leg up on this. They're desperate for information but also desperately overwhelmed by jargon."
Taking further steps to prevent access is another approach. Even when parents do manage to prevent their children viewing and sharing porn at home, they can't be sure they aren't doing so elsewhere. So a measure to prevent them accessing it, wherever they are, must be sought. Mr Findlater says: "Newsagents have to put their porn magazines on the top shelf. Where's the top shelf for internet porn?"
* Not her real name