Some men who are sexually attracted to children would like help to change their condition but fear doctors will tell the police. In Germany, though, a campaign is under way to persuade them to sign up for confidential treatment, even if they have abused a child - and doctors are hailing it as a big success.
Max is a science graduate, in his early thirties. Articulate, with a ready smile and an infectious laugh. He could be your neighbour, your work colleague or your sister's new boyfriend. A nice guy. An average bloke. Except he's also a paedophile.
Max is sexually attracted to pre-pubescent girls — typically between the ages of six and 11. It's an urge that for years filled him with self-loathing and despair.
"I would see a girl, and I would undress the girl in my mind, and it was just disgusting, and I'd say to myself: 'Stop this.' And it just wouldn't stop. I had feelings of disgust and fear," he says.
Max has never abused a child sexually, nor does he consume child pornography — itself a form of indirect abuse, because children are usually involved in its production. In fact Max is just one of many people who feel an attraction to children, but who are determined not to act on it.
They are sometimes called celibate or "virtuous" paedophiles. The word "paedophilia" describes the sexual attraction, not the abuse itself, so not all paedophiles are child abusers - and not all child abusers are paedophiles, experts say, since abuse sometimes has other root causes.
Celibate paedophiles are a hidden segment of the population. They have never committed an offence, so are unknown to the police. And because of the taboo - and the fear of violence from people who think they are child abusers - they usually keep their attraction secret.
It's a much bigger group than you might think. Recent research suggests that between 3% and 5% of men, from all social and economic backgrounds, could be sexually attracted to children. Some are attracted only to girls. Others only to boys. Others to both. And some are also attracted to adults.
"I don't have greasy hair, pebble glasses and wear tatty clothes," writes Max in a book he has published to help other paedophiles who don't want to abuse children. "There is no such thing as the typical paedophile which people imagine. We are all different, and completely normal people. The only thing we all have in common is a sexual attraction to children… I am learning to control the sexual side of my feelings."
He's doing that partly thanks to a radical treatment for paedophiles called the Dunkelfeld Prevention Project, which is in operation at 11 different centres across Germany.
For a year he attended group therapy, three hours every week.
"It was very painful," he tells me. "It was about getting to know a side of myself that I had hidden, a side that I didn't like to think about. It's painful to acknowledge that you are a paedophile. It was like standing in front of a mirror, and on the one hand thinking: 'What kind of a monster are you?' But it was also very healthy to stand in front of the mirror and say: 'I'm a paedophile, but that's OK, I won't do anything bad.'
"A very important thing is acceptance. To be able to think and feel that paedophilia is a part of me, but it's not what defines me. My actions are what define me."
The treatment is a form of cognitive behavioural therapy which analyses past sexual behaviour and feelings, in order to come up with strategies to avoid potentially abusive situations in the future. Some practical advice is very simple, such as never being alone with a child. Other tactics are more complicated, and involve changing attitudes, for example helping the patient to grasp that sexual contact with children can never be consensual.
Controversially, the treatment is also available for men who have abused children in the past — even if that abuse has gone unreported.
So what does a therapist do if a patient says he has abused a child?
"If he comes to us and says, 'I have done something illegal in the past and don't want to do it again,' and that's the normal case for us, then we can help him to build up his self-regulatory behaviour to not do that again," says clinical psychologist and sexologist Anna Konrad of the Charite hospital in Berlin.
But surely, I suggest, it's difficult to sit opposite a man who has abused children and try to help him?
"The main aim of the project is to protect children from being abused, and if I can help the person not to do that again, then for me it's quite clear that I should do that," she says.
In Germany, therapists are not only not obliged to report past abuse to the authorities, it is illegal to violate the principle of patient confidentiality - unlike in Britain, where therapists have a duty to report.
The British approach makes it extremely difficult to treat someone properly, Konrad says. The past behaviour of abusers can't be analysed effectively, and paedophiles rarely come forward for treatment in the first place because of the fear of arrest - if they have committed a crime they are right to be afraid, and even if they haven't they may still consider it too risky.
Max agrees with this.
"A treatment like this can prevent the first offence. Criminalisation — if it works very, very well, and it usually doesn't — can only prevent the second offence," he says.
More than 430 men have started the treatment. And because of a lack of places, there are long waiting lists. Since it was first set up in 2005 more than 5,350 people have contacted the network for advice or to find out more about the therapy. Anna Konrad says patients are asked to fill in a questionnaire at the start of the treatment and at the end - and that a comparison of the two suggests the success rate is good.
There is even a national advertising campaign to tell paedophiles about the treatment.
"I always knew that I was different, and what others thought about people like me," say masked men in a television commercial — one dressed as a doctor, another as a workman, another as a student.
"No-one is guilty because of their sexual inclination — but everyone is responsible for their behaviour," says the final young man as he takes the mask off, adding: "I don't want to become an offender."
The tagline of another ad says: "Do you love children more than you'd like to? There is help."
The idea behind the policy is not to help the perpetrator instead of the victim — but rather to help the potential perpetrator, in order to prevent there being a victim in the first place.
You can listen to this report on the PM programme on BBC Radio 4 from 17:00 BST on Monday 13 July, or catch up afterwards on the BBC iPlayer.
Subscribe to the BBC News Magazine's email newsletter to get articles sent to your inbox.