From such idle moments can a life unravel. Last Friday the pop star Gary Glitter was sentenced to four months in prison for this offence. In British law, the act of downloading a pornographic picture of somebody who is, or even appears to be, under 16 is an offence under the Obscene Publications Act. Having that picture on your computer's hard drive is an offence. A number of people - to be precise, men - have been charged under the OPA when they have taken their computers to shops for repairs and the technicians have found the pictures on the disk. The computer's owner may have thought he had covered his tracks by deleting the pictures; he may even protest that he just viewed the pictures online. However, the web browser used to view them also downloads them, to a temporary file called its "cache" - on the hard disk.
So much for the mechanisms of discovery. But the key questions that governments and other organisations involved in the care of children are asking are: is the internet's instant access to a cornucopia of data actually encouraging the demand for child pornography? And is there any way of stemming the supply, or its distribution, while allowing the free flow of truly useful information?
On the first point, the answer does seem to be that by making a wider variety of experiences quickly available across national boundaries, the internet is feeding desires that would otherwise be latent.
Allan Levy QC, a family lawyer, thinks that some internet users, bored by conventional pornography, cross the line in search of new thrills. "They may not have a sexual preference for children, but have seen the range of adult pornography and are seeking more unusual material," he said. It is also much simpler to log on and search than to find a shop selling such magazines: "Anonymity and ease of dissemination and retrieval have revealed a disturbing level of sexual interest in children."
The shift has been reflected in the materials recovered in police raids. In 1984 when the police smashed the post-based Paedophile Information Exchange, they would recover a few photos and some videos. Last year, in Operation Cathedral, 96 homes were raided in 12 countries: in the US homes alone, half a million indecent images of children were found.
Mr Levy, who chaired the Staffordshire "pindown" inquiry into abuse in child care, said: "One of the greatest concerns is that the internet has made child pornography more visible and accessible, giving paedophiles and other interested parties what one observer has described as `the sense of being connected to a community of like-minded individuals'."
Who produces these images, and why? It is not, in general, the commercial adult sex sites where access is paid for by credit card. As every police force in every country has people whose full-time job is finding child pornography sites and tracing their users, commercial sex sites do not want the hassle.
Evidence from the few court cases involving producers of child pornography suggests that they do it because they enjoy it. Often the images started on paper and have been scanned in. Others are photographs exploiting children who may be in care. "Children in care are at risk of being, and actually are, involved in child pornography and prostitution," Mr Levy said.
To enter the closed world of the web paedophiles, the price of access is often to supply an obscene picture yourself. This forces you to cross the line: you become like-minded with the paedophile. Most worrying is the fact that those who suffer sexual abuse as children are far more likely to commit it as adults. In that sense, child pornography directly threatens the happiness of future generations.
However, the weapons available to governments to tackle such sites are limited by the network's global sprawl. A website and library of obscene images can be shuttled from computer to computer, country to country, in a couple of hours.
Australia has tried outright censorship of the internet, by declaring that certain content is banned. Its status as an island makes that temporarily possible; but the law imposing it is plainly flawed, for satellite communications and the techniques for "burrowing" on the internet can be read by anyone. Australians can circumvent the law easily: log in to a permitted site; "burrow" from there to a banned site; and copy the data back to the permitted site.
Another possibility is to incorporate tracking systems into the next generation of the "internet protocol", which every computer hooking up to the net uses. The proposals, due to be debated later this month by the Internet Engineering Task Force, could mean that everyone using the net would have a single number that would identify them.
That could make it simpler to track down paedophiles by monitoring electronic traffic. But it also raises questions about security and anonymity for law-abiding people. Evan Hendricks, editor of the US-based Privacy Times, comments: "The potential for abuse is too great. It will be like a fingerprint embedded in the data that can be traced to the net user."
You may think that that would be fine to catch paedophiles. But do you want the police, or just persons unknown, to be able to find out everything you have looked at on the net? The knife cuts both ways.
n Additional research by Emma Burns.
CYBERSPACE VOTING, PAGE 26
Tabloid defends its role
TWO investigations are under way into allegations that the News of the World prejudiced Gary Glitter's indecent assault trial by making one payment and offering another to the key female witness.
The Lord Chancellor, Lord Irvine of Lairg, has asked the trial judge, Mr Justice Butterfield, for a full report on allegations that the newspaper paid Glitter's alleged victim pounds 10,000 for her story and offered her another pounds 25,000 if Glitter was found guilty.
Lord Irvine said: "Payments to witnesses, or potential witnesses, by the media run a real risk of encouraging witnesses to exaggerate their evidence to make it more newsworthy, or to withhold relevant evidence from the court and make it available as an exclusive to a newspaper."
The Press Complaints Commission is also looking into whether the newspaper breached the regulatory body's code of practice. The News of the World welcomed the investigation and denied breaching the industry's code.
The Liberal Democrat peer Lord Carlisle is calling for legal restrictions on newspapers paying witnesses.Reuse content