The service is known as Oboe and is being offered via MP3tunes.com. It has been set up by Michael Robertson, who is known as the founder of MP3.com.
Users paying $39.99 a year can use Oboe to copy their entire music library in to what is being described as an "online music locker", which Robertson says can be used to store the music securely, safe from hardware malfunctions, viruses or theft.
The service works by searching an entire computer for music files and then loading all the files into the locker. It will work for MP3 files, as well as iTunes and Windows Media, and works with Macs, Windows and Linux.
There is also a free version that allows users to store and play an unlimited amount of tracks from any free music source on the net.
"Five years from now, lugging around your entire music collection and plugging it in everywhere will seem as outdated as carrying around a pocketful of nickels," Robertson, CEO of MP3tunes, said.
"It makes more sense to safely store your music online and sync it or stream it to all the places you listen to music, which is exactly what Oboe makes possible."
However, the introduction of the service has raised speculation that it could attract the attention of record companies concerned about copyright. The service has been developed with the involvement of a programmer called Jon Lech Johansen, known as DVD Jon. He has been taken to court over allegations that a programme he developed has been used to illegally copy and distribute DVDs, but the charges have not been proven.
Robertson has conceded that users can potentially share their password and music files with others.
However, in an interview with the Financial Times, he said: "There may be controversy about this. But we really don't know what content is going in. We are a service provider and not a whole lot different from Gmail."
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