How shall we know them? Abusers' psychology remains the same, but technology is making their menace more complex.
SITTING in a stuffy room on the 6th floor of a city office building, Detective Senior Sergeant Debra Bennett is trying to explain the difference between a child molester and a paedophile.
You only have to witness the public fury that led to the recently announced royal commission on child abuse to understand the almost primeval feelings aroused by those who prey on the young.
Most people cannot conceive of committing this type of crime, and would find it difficult to understand what motivates a child sex offender.
But for Bennett, an FBI-trained forensic psychologist, it's a crucial part of her job.
Bennett works shoulder to shoulder with the 12-strong Astraea taskforce, formed earlier this year to hunt down child sex offenders, who use the internet to find and abuse their victims.
The taskforce works closely with police forces in other states, national law enforcement bodies such as the Australian Federal Police, Customs and the Australian Crime Commission, and overseas agencies.
Since Astraea was formed, dozens of men of all ages and from all walks of life have been arrested and charged with offences such as possessing child pornography and grooming children for sex.
During a lengthy interview with Fairfax Media, Bennett explains that not all child sex offenders are the same: just as they come from all areas of society, they have different motivations.
At one end of the spectrum, she says, are those who prefer to have sex with children - or paedophiles - while at the other are people who will have sex with children because of the particular situation they find themselves in.
''It could be just out of curiosity, it could be because they don't feel as if children are going to judge them like adults will, it could be that they'll have sex with anything, and children are just one of the spectrum, it could be a revenge-type scenario - he's in a relationship with somebody but feels disaffected in some way, doesn't have any power or control, feels as though she's dominating.''
Bennett spent four years training with the FBI, studying the motivations and behavioural signals of arsonists, kidnappers, sex criminals and killers, and went on to obtain a doctorate in psychology.
The genuine paedophile is the most difficult to treat, Bennett says, because he truly believes that what he is doing is not immoral, and that the victim is consenting.
She says paedophiles can be brought to a point where they understand that society finds what they do unacceptable - whether they agree or not - and therefore that they have to stop.
Bennett also advises the courts in a private capacity before culprits are sentenced, which sometimes requires interviewing and assessing child sex offenders. She is careful to stress that her next comments are made in that capacity, rather than that of a policewoman.
''For the older guys, it's ingrained, they've convinced themselves they're not actually doing anything wrong,'' she says. ''Then they meet other like-minded men, then pornography reinforces that.
''Then what do we do with them? We put them in Ararat prison, we put four men in a cell, shut the door at 6pm and hope that nothing's going to happen before the morning, and then they're going to be cured before they leave. That's not going to happen.''
Understanding what makes ''child molesters'', as opposed to paedophiles, tick is more complex. Bennett estimates that 99 per cent of offenders in this category will initially refuse to discuss why they committed the offences.
''In general, sex offenders have no idea why they've done it. They really don't want to look at it, they don't want to sit down with a middle-aged woman and talk about their porn collection or fantasies. They prefer for it to just go away. If they do look at it, they're kind of obliged to do something about it if they don't want to reoffend. But if you don't work out your own offending cycle, then the chances of you being able to hold back from reoffending are slim because you don't understand the cycle in the first place.''
Astraea was formed as a direct response to the seismic effect the internet has had on the ability of offenders to procure child abuse images and actual victims.
In the past nine months, the taskforce has conducted 80 investigations, resulting in more than 50 arrests. It has also referred over 20 investigations to other jurisdictions in Australia, the United States and United Kingdom, a testament to the absence of borders online.
The culprits will often trawl through social media, looking for children they believe will be susceptible to approaches. They then ''befriend'' and groom them, developing trust and eventually convincing them to post ''sexualised'' pictures of themselves. The head of the taskforce, Detective Senior Sergeant Rob Ridley, said police officers posing as children online were sometimes approached within minutes of logging on.
''When they get them talking they'll try and make them feel special, they'll try to ostracise them from an authority figure. When you think about it, it's pretty similar to what used to happen with face-to-face contact, but if you play the numbers on the internet there are more chances for you. Once they have the image of the child in a sexualised pose, they try to ramp it up, blackmail them into meeting them. A lot of them think they've got them then, because they've got the photo of them doing something sexual and they've had that sexual talk beforehand, and then they'll meet them for a contact offence.''
Ridley says the downloading of child pornography is ''out of control'', with the videos and still images becoming more extreme and showing increasingly young children.
The proliferation of smartphones and tablets has also made it more difficult for parents to keep tabs on who their children are communicating with. Gone are the days when police could effectively advise parents to keep the home computer in a communal area of the house. Ridley also says there is no type of child more vulnerable than another: victims come from all sections of society, and from different types of families - not just broken homes, as is commonly thought.
While there is no doubt the internet has facilitated offending by those who would arguably have offended anyway, it is also clear that it has increased the likelihood of people graduating from viewing child pornography to abusing children.
''That's definitely a question that comes up out of this,'' Bennett says. ''Does having access to this much porn increase the risk of people committing these offences?
''Research is showing that pornography is by far the biggest indicator of what a person's actual preference is, and that if you have lots and lots of porn, it's not going to help you in not reoffending. It can increase your likelihood of recidivism if you're already an offender.
''For someone who's viewing a lot of child porn, they're definitely going to be more at risk of committing offences against children. The more you see of anything, the more acceptable it's going to become, no matter what it is.''
Ridley says the Supreme Court of Canada made a clear link between viewing child pornography and going on to physically abuse children, and that studies suggest between 50 per cent and 60 per cent of people who possess images or video eventually commit contact offences.
A more fraught question is whether viewing ''normal'' pornography leads to child pornography and actual sexual assaults on children.
''Some of the cases we've had, you'll hear an offender talking about how he started off viewing 'legal' porn, got to more bizarre things, moved on to bestiality, then children, and then moved on to contact children and offend,'' Ridley said.
''He started with pornography at around 12 or 13, and then by the time he's 21 or 22 he's trying to get kids through the internet.''
Bennett makes the point that it does suit some to claim they started watching standard pornography and graduated to child abuse material, because they believe it shifts the moral culpability away from them.
In sentencing the former ABC presenter Andy Muirhead to 10 months in prison for downloading child pornography, Tasmanian Supreme Court Chief Justice Ewan Crawford last month rejected a psychologist's claim that Muirhead had no sexual interest in children, and was viewing the material because he was stressed.
''I must observe that final conclusion was based on his self-reports which, I have concluded, were not truthful,'' the judge said.
''I am satisfied that he has a sexual interest because of the quantity of the material downloaded by him, its nature, he downloaded it on numerous occasions exceeding 15 months.''
Bennett is sceptical about claims that excessive viewing of ''normal pornography'' can lead to an interest in child abuse material, saying that people do not develop a sexual interest in much younger children ''at 16 or 21''.
She says it most likely stems from something in the offender's childhood, and that tackling the early indicators of a sexual interest in children when they first manifest can stop offending later in life.
''Identifying them at that age is what we need to do, because they don't make it to 16 without anything being there,'' she says, again speaking in her private capacity as a psychologist. ''The alternative is we build another prison and fill it.
''There have been indicators along the way, and if we're able to correct them back there, that's going to change so much for us.
''Research does show that the greatest percentage of people who commit these offences have been offended against themselves.''
When discovered, Ridley says, some child pornography users express relief, because they did not believe they would be able to stop by themselves. Others simply don't care, and express no remorse.
When asked whether he believes child sex offenders are intrinsically evil, the softly spoken and thoughtful Ridley pauses for a long time.
''I've read the studies,'' he says. ''I think there are some who are intrinsically evil, and I think there are some that aren't.''
Does such expertise in the psychology of abusers and victims come at a high personal cost?
''I try to realise I've got a job to do and not personalise it,'' Ridley says. ''That's what we're here for. If you're going to sit there and it does concern you to the extent that you do personalise it, and you're thinking about it all the time, then you're in the wrong job.
''It is a concern for our members, their welfare, because they're looking at pretty horrific images and dealing with horrific stories, but we do have a psychological program they go through, testing and screening, visits by psychologists. So it's about getting the right people at the start and then supporting them.''