The world's biggest music group has agreed a deal to make its catalogue available on a free legal downloads service aiming to rival iTunes.

Universal Music's tracks will appear on SpiralFrog, which is set to be launched in the US and Canada in December. The service will make money from adverts on its site rather than charging people to download music.

American internet users currently pay 99 cents (52p) per song on iTunes.

"Offering young consumers an easy-to-use alternative to pirated music sites will be compelling," SpiralFrog CEO Robin Kent said.

"SpiralFrog will offer those consumers a better experience and environment than they can get from any pirate site."

According to the International Federation of Phonographic Industries (IFPI), 60 million MP3 players were sold last year and 420 million single tracks were downloaded during the year.

That figure is up to 20 times higher than it was two years ago.

But for every legal download, it is estimated that 40 are done illegally.

Mr Kent said the company's research revealed that consumers were "more than willing" to effectively pay for their content by watching "non-intrusive, contextually relevant, targeted advertising".

SpiralFrog's target audience, people between 13 and 34, was an advertiser's dream, he added. He said users would benefit from downloads that were free from viruses or spyware.

"We want to provide the best environment for everyone - our partners and the recording artists, as well as consumers," Mr Kent added.

"Piracy continues to be one of the biggest issues facing the music industry where illegal file sharing and unauthorised CD burning are the prime means.

"Digital rights protection will help us combat piracy and provide peace of mind for record labels and artists."