Jon Lech Johansen, who runs a software company in San Francisco called DoubleTwist Ventures, said yesterday his program would fool computers into thinking that any MP3 player was an iPod. He said it would also make any piece of music or video downloaded from the internet appear to have been bought from iTunes.

Music bought from Apple’s iTunes online store can be played only on the company’s own iPod devices. The songs, music videos and movies bought on iTunes contain a security code that prevents them from being played on rival media players.

The iPod also blocks music bought from other online services such as Amazon.com.

Mr Johansen, a self-trained software engineer, is one of the world’s most notorious hackers. He was accused of breaking the coding that protects DVDs from being copied - a hack that Hollywood claimed cost billions in lost revenue - but was acquitted of all charges after a lengthy trial in Norway.

Apple has yet to respond to Mr Johansen’s claims, but it is understood that the company’s lawyers and software experts are examining them to see if legal action can be taken.

DoubleTwist Ventures said it had sought legal advice and believed that the hack was entirely above board and commercially viable.

The French Government recently passed a law pressuring Apple to allow music sold by other online providers to be compatible with iPods, but it contained a loophole that allowed Apple to continue to block music from other services.

But after the French case, other European countries, including Sweden and Denmark, are considering legislation to thwart Apple’s exclusivity.