Britney Spears is among the pop stars fronting a new advertising campaign aimed at warning people against online piracy.

Rapper Nelly and hip-hop star Missy Elliott will also be featured in the campaign, which will be screened on TV in the United States over the next few months.

It has been funded by the world's biggest record labels to educate people about illegally downloading music off the internet, which is being blamed for a dip in sales.

According to industry estimates, over 2.6 billion music files are downloaded illegally every month, mainly through unlicensed "peer-to-peer" services.

CD sales reportedly dropped by 7% in the first half of 2002.

Stealing

"We want to hit fans with the message that downloading music illegally is, as Britney Spears explains, the same as going into a CD store and stealing the CD," said Hilary Rosen of the Recording Industry Association Of America (RIAA).

"Too many people don't realise that when you download a song you like from a peer-to-peer network or some other unauthorised internet service, you're stealing music," she said.

Missy Elliott is also involved in the campaign

The TV adverts will be shown at a Congressional hearing on piracy in Washington on Thursday before making their debut on US screens a few weeks later.

A print campaign, featuring such performers as Eminem, Madonna, Missy Elliott, Elton John and Luciano Pavarotti will be launched in major American newspapers and magazines this week.

Napster

Downloading music off the internet first became popular with the launch of Napster, which attracted tens of millions of users at the height of its popularity.

The service finally closed earlier this month after a judge blocked its sale to German record label Bertelsmann - but a number of bidders have since come forward offering to save the site.

A raft of file-sharing alternatives has also emerged, among them favourites like Kazaa, Audiogalaxy and Morpheus.

Kazaa, by far the most popular software, now has about 8.2 million US users, according to internet tracking firm Comscore Media Metrix, not far off Napster's peak of 13.6 million.