Philip Rosenthal treats people with addiction. However, his field is specific - he does not deal with drugs, alcohol or gambling but rather a compulsion which he feels is increasing exponentially.

The former United States police officer's speciality is addiction to technology. This usually takes the form of compulsive internet usage, although he has also treated addictive texters. "Basically," he says, "if it runs on batteries or plugs into the wall, I treat it."

The problem with technology addiction is how to define it. After all, we are all increasingly dependent on computers and mobile phones, and spend many hours a day staring at screens. So when does it become a problem?

Rosenthal says that the warning signs will be clear. If you are sitting surfing away for hours while your family is having dinner together, you have a problem. If you have been warned at work for inappropriate internet usage and you still feel compelled to go online, you need help.

"Addiction is addiction. It ruins your family and affects your entire life. Addiction is any activity you are compelled to repeat. How many times have you sat down to Google something and realised that two hours have gone by? With cocaine, you carry on sniffing until your nose falls off. With the internet it means: 'I need to see another movie, another image. I need to keep sending texts and receiving texts. I need that validation because I feel empty without it.'"

Part of the problem, says Rosenthal, who has been working in the high-tech industry for 30 years, is the pervasiveness of the technology. He places his iPhone on the desk in front of him. "There is probably 100 times more power in this device than in the computers that put man on the moon. It has to be used wisely. The internet is not a magical, mysterious place. It is just a microcosm of our world. It is more efficient than the ways we used to do things but it can get you into trouble more efficiently, too."

Rosenthal, who was in London recently for a series of events organised by Ezer North West -which provides counselling and support for the Orthodox community - had no intention of becoming a cyber counsellor. Nor for that matter did he have any ambition to become a police officer. But his career path has taken him to some unexpected places.

"I graduated in broadcast journalism but I needed a job and someone said to me, 'you look like the kind of guy who might be good with computers', and the rest is history. Twenty years ago I segued into law enforcement. I became a computer forensic investigator. At the time there were probably fewer than 50 people like me in the world. At the ripe old age of 40 I became a police officer. Despite a debilitating form of arthritis I did the runs and the calisthenics, the defensive training and the shooting. Thank God for pain-killers and hot baths," laughs Rosenthal, who with suit and kippah, looks anything but the stereotypical New York cop.

Part of his police work involved community outreach work. He began to do 20-minute presentations on what was happening on the internet.

"I was a halfway decent public speaker and people got enjoyment from my presentations. One day I got a call from a Jewish organisation asking if I would do a talk for them."

His presentation impressed one of the other speakers that night - the revered Orthodox psychiatrist Rabbi Abraham Twerski, who persuaded Rosenthal to "take his show on the road".

"The more I spoke, the more it grew and it began to get out of hand. Rabbi Twerski asked me if I would train to counsel people for this. He said he was passing me the torch. I told him that I was not in receiving mode. But he is a very hard guy to say no to so I went back to school, got my masters and left the police about a year ago."

Rosenthal uses a form of cognitive behavioural therapy to counsel victims. He is particularly concerned about children whom he thinks are especially at risk from new technology, not least because they understand it better than their parents.

"This is the first advancement in the history of mankind that children know more about than their parents do. Our children are digital mavens. They were born into it. You say to your kids, 'listen, I know what you've been doing on your phone', and they say, 'I didn't do that, I did this', and you are so intimidated that you don't challenge them on it."

However, parents should not be scared. What they need, says Rosenthal, is a little knowledge and good parenting skills. "Kids are totally at risk. They are naïve, they are trusting. You cannot treat the internet as your babysitter." Rosenthal, while emphasising that no precaution is foolproof - particularly when your children get into their teens and start to develop advanced computer skills - says there are steps parents must take. "If you don't teach your kids to look both ways when crossing the road, they'll be hit by a truck - it's the same with the internet."

He is adamant that parents cannot take chances with their children's safety. "Never put a computer in a child's bedroom. And if you have no other place to put the computer, then take the door off its hinges. If they can close the door they are going to do something bad in there ultimately."

There are other precautions parents must take. "First is to put a filter on the computer. It should literally be a crime not to. If you go to Fox News and misspell it you could end up on a Russian pornography site. No child should be subjected to that. Filters like K9 are free - it is irresponsible parenting not to have one. You can decide on the level of severity."

Rosenthal also suggests that parents invest in monitoring software which will transmit to them every keystroke their children make, from emails through to instant messaging.

But he does emphasise that whatever precautions you take, there are no real solutions. "Any one of these filters can be bypassed. If they want to be bad, there is nothing you can do."

So there is need for constant vigilance. "Parents have a feeling for when their kid is out of sorts. If a kid is normally outgoing but seems withdrawn, it's up to you to find out what is going on. You also have to warn them about the dangers of strangers grooming children on the net. There are people who say that talking to their kids about this stuff will make them more curious. But I say that it is a parent's job to warn children about what can harm them. It is worth the risk."