Hollywood stars are launching an attack on Internet sites that make money by showing fake or stolen nude pictures of celebrities.

Alyssa Milano, 25, an actress from the long-running soap Melrose Place, filed two lawsuits in Los Angeles Tuesday against several sites she says show pictures of her naked.The action is the first of its kind and is regarded as a test case against a growing industry exploiting digitalized nude images that are often flagrant violations of copyright - or outright fraud.

Milano's Beverly Hills lawyer, Michell Kamark, said: "Celebrities are realizing for the first time that the Net is a dangerous force if it's not corralled. We hope that this suit starts a broader attack by Hollywood against such sex sites."

One of the defendants named by the actress is John Lindgren, 21, who claims to make around $10,000 a month from his Web site, run from Minnesota.

Rather than going to the expense of defending himself, he said he would remove the Milano pictures but would continue the business using other stars' pictures.

Many of the pictures are made by grafting the head of a star onto a nude photo of someone else. A homemade gallery of nude images can be created using relatively simple desk-top publishing equipment.

Taking pictures from a film is trickier and a direct infringement of copyright. Some pictures are copies of paparazzi shots.

The sites make money by charging access fees, selling the pictures online for about $100, or making more elaborate and expensive CD-Roms with hundreds of pictures. Customers give a credit-card numbers and another company that checks their veracity will also verify that the buyer is not a minor, one of the few legal requirements in the burgeoning Internet porn business.

Although the law may be in Hollywood's favor, closing down the electronic peep-shows is probably impossible. The Internet is almost completely unregulated and the astonishing proliferation of pornography in cyberspace is testament to the genre's popularity.

But the stars are outraged and their resources are immense.

Milano's mother, Lin Milano, started a company to identify and pursue cyberporn pirates after her 12-year-old son accidentally found pictures of his famous sister in the buff on the Internet.

Defendants of the sex sites argue that they come under the "fair use" legal exception, by which publication of copyright images is permitted if they are presented in the context of news or commentary - a protection exploited by magazines that run "nudes in the news" celebrity pictures. But the argument is implausible on the Internet as the sites make no effort to provide a news context.