Twenty years ago, a predatory paedophile would have had to loiter around parks, funfairs and swimming pools to gain access to children, where his suspicious behaviour - in full public view - would often have raised the alarm before he could cause any real harm.
But computers and the internet have brought an end to all that.
Since 2005, it's been using officers posing as young girls in internet chatrooms and on social networking sites to draw these paedophiles out into the open.
The idea is not to entrap them (which would be against the law), but simply to communicate with them long enough for them to break the law, either by engaging in sexual grooming, sending indecent images to a minor or by encouraging them to commit an indecent act.
Somewhere out there, as you read this, a man sits hunched over his computer, his brow furrowed in concentration as he taps away at his keyboard.
But he's not booking cinema tickets or tracing his family tree or doing any of the things that have made the internet such a valuable tool of modern life.
No, the sickening truth is that he's pretending to be a 13-year-old girl and he's in one of those internet chatrooms so beloved of our teenagers. The man, of course, is a paedophile; one of the most feared and loathed figures in today's society. well, she could be my daughter, your daughter or anyone's daughter.
Yes, child protection officers do still come across the sad and dangerous individuals who could be described in that way, but increasingly they are arresting a new breed of paedophile.
That's what happened when Andrew Lintern logged onto an internet chatroom pretending to be a nine-year-old girl and began a conversation with 'Jessie', whom he believed was a 13-year old-girl.
Only, just as the nine-year-old girl wasn't who she said she was, nor was Jessie.
Often married and with children themselves, they can be well-educated and highly successful in their field.
Passing them in the street - and it could easily be street - you wouldn't give them a second glance.