It is an emerging form of Internet fraud and now the United States has started legal action against its perpetrators.

The director of NewWorld spotted the "page-jack"

The Federal Trade Commission has secured a preliminary injunction to restrain people from "page-jacking", a practice whereby Internet users are diverted from material they want to view to other pages from which they can hardly escape without rebooting their computers.

New browser windows with porn content pop up faster than they can be closed down, and as many people do not know how else to close down their Internet browser application, their computer is taken over by the page-jackers.

The owners of Websites that the users are diverted to are then able to earn more money from advertising.

"Pagejacking" is done by the cloning of legitimate Web pages with the invisible metatags that are used to index them for the search engines.

'Millions of sites at risk'

FTC director Jodie Bernstein: "We cannot monitor the Net alone, but we've got help."

FTC director Jodie Bernstein says that 25 million Internet sites could be vulnerable - an estimated 2% of all sites.

She says that the practice could undermine the viability of the whole Internet system.

The FTC began the court action after the Texan Internet company NewWorld complained that a Website it had designed for teenagers and children had been page-jacked by pornographers.

To escape detection, the fraudsters move fast, reinventing themselves every few hours.

Prominent targets

The FTC obtained a restraining orders against a pornographer in Portugal and another in Australia.

The commission holds them responsible for page-jacking incidents not only at the NewWorld Website, but also those of the Harvard Law Review, carmakers Audi and others.

The FTC argues that page-jacking constitutes deception and unfair trade.

Trapped

The sites were set up in such a way that users could not leave the sites by clicking on the "back" or "home" button.

Instead they were connected to another pornographic site in a practice which has been dubbed "mouse-trapping".

The FTC's Bureau of Consumer Protection is particularly concerned that criminals clone Websites of special interest to children who are inadvertently routed to pornographic sites.

Jodie Bernstein of the FTC says the commission cannot monitor the whole of the Web, but "we have very able partners in the states that co-operate with us and also in various industries."

As part of the investigations in Australia, several premises were raided.

The Australian authorities have said they are considering civil or criminal charges against the pornography company involved.