The US entertainment industry is using pop-up messages to threaten users of peer-to-peer (P2P) music download systems.

Upset at the recent setback in their legal fight with file-swap software firms Grokster and StreamCast, industry associations have adopted instant messaging technology to warn music fans logging on to P2P download sites that they are breaking the law.

Thousands of people have received the unsolicited message which reads: "When you break the law, you risk legal penalties. There is a simple way to avoid that risk: DON'T STEAL MUSIC."

Cary Sherman, president of the Recording Industry Association of America (RIAA), is unrepentant about the campaign.

"People feel invincible when they're doing this in the privacy of their home. This is a way of letting them know that what they're doing is illegal," she said in a statement.

But Sharman Networks, the distributor of Kazaa software, another P2P system, claims that the action breaks privacy laws.

"We strenuously object to efforts outside the law, in violation of user agreements, or in violation of privacy rights, to indiscriminately spam, mislead or confuse," the company said in a statement.

Meanwhile, the RIAA has received permission from a federal judge to force internet service provider Verizon to turn over the name of a subscriber it suspects of providing hundreds of copyrighted songs through Kazaa.

Verizon is appealing the decision but if it loses it could result in ISPs being forced to hand over the names and addresses of other web users it believes are illegally downloading or sharing music files.

It has also filed lawsuits this month against four US college students, charging them with copyright infringement.

Initially - and unrealistically - the RIAA was seeking millions of dollars in damages from the students.

But it has now settled on fines ranging from $12,000 to $17,500 which the students can add to their college loans and pay back over the next three years, according to Associated Press.