De Sade would have loved the internet

There was a time, around two-and-a-half years ago, when parents up and down the country were dismayed to discover that their teenage children were enthralled by an angry young man with a leather mask and a chainsaw. Apart from his fantasies about dismembering his estranged wife, Eminem (pictured below) was the archetypal teenager: pissed off with his mum, trying out scary new identities and bearing a grudge against the entire world. That is why he appealed to so many kids who fantasised - as adolescents have always done - about running away, being someone else or finding a friend who really understood them.

In the past, those dreams existed in their own heads or filled the pages of anguished diaries. Now the internet has enabled them to project their discontents, longings and identity crises into cyberspace, where they can be picked up by literally anyone. In the past few days, much has been written about the safe return from Germany of a 12-year-old girl who left the country with a former US marine she "met" on the internet, but it is clear that the case of Shevaun Pennington is not an isolated one. A second girl, 14-year-old Jenna Bashir from west London, who ran away for two weeks, was found to have posted photographs of herself on the internet and describing herself, in street slang, as a sexually experienced 17-year-old.

Jenna's anxious parents fear that she has been lured away by someone she encountered in a chat room. The internet is rapidly coming to occupy a place near the top of parents' fears: stranger-danger invading the family home, through the innocent-looking mechanism of a computer portal. Adults with a malign interest in children and teenagers can now rely on a modem instead of hanging round school gates, and it is not always easy for parents to get the message across that it is dangerous to pose as someone older and more experienced. Yet it is also clear that this is part of a much wider phenomenon, and we have yet to grasp the extraordinary impact of the internet on fantasies that used to be - and for many of us still are - a very private part of everyday existence.

There is not necessarily anything wrong with fantasies, many of which are romantic, erotic or a way of living with slights and disappointments. Eminem's reinvention of himself as a kind of suburban avenger has made him a lot of money and, arguably, defused feelings of anger and alienation that might otherwise have become unbearable. But there are not many Eminems in the world, and the internet is a much more practical avenue of release for bored and lonely teenagers. At the same time, the success of the Friends Reunited website demonstrates that it is not just adolescents who dream about meeting a kindred spirit in cyberspace, although in this instance the fantasy (another money-spinner for its inventors) is about recapturing lost youth.

The problem with the internet - and I think it is a problem, in spite of all the advantages associated with the technology - is the way it encourages those fantasies to move from private to public space. Everyone feels safe, sitting at home with a computer, which may be why so many people are willing to type intimate details about themselves on to the screen. Yet they are exposing themselves to strangers who may be sick, possess a string of criminal convictions and have gone to some lengths to disguise their true identity. It is no more sensible than pouring out your sexual fantasies to the man or woman sitting next to you on a bus and then agreeing to go home with them, yet the circumstances disguise the risks.

In a world where everyone is encouraged to seek instant gratification, the internet has made fantasies seem much more attainable. In reality, this is mostly an illusion, as anyone can tell you who has actually arranged a date with someone they encountered by this method. Even if the experience isn't actually dangerous, it is often acutely disappointing, as people's lies about their age, appearance and personality are exposed. There is also a question about how healthy it is to spend so much time avoiding real life and ordinary people, with all their positive and negative characteristics. You may dream of finding a soul mate on the internet, but I'm sure that the prospect of spending hours in a chat room would have thrilled the Marquis de Sade.