Online music service, eMusic sold its 100-millionth music download this week, proving the case for selling tracks free of digital rights management (DRM) restrictions on use.

The subscription service claims to be the second-biggest online-music-to-own store in the world. It sells tracks in MP3 format, free of DRM, with most of its catalogue provided by independent music labels.

While its sales are dwarfed by those of industry leader, iTunes, eMusic's success proves that music fans will buy unprotected tracks.

"Except for iTunes, the only store that is doing well online with downloads is eMusic, and the reason is because they do sell it without (playback restrictions)," Inside Digital Media analyst, Phil Leigh, told Associated Press.

Other services that sell their music in DRM-protected Windows Media formats haven't achieved the same level of success.

UK online music provider, Wippit, sells tracks in both WMA and MP3 formats, and has noted that where a track is available in both formats, the MP3 tracks outweigh sales of WMA files by a factor of five to one.

EMI recently released three tracks (two in the UK, one in the US) in DRM-free MP3 formats.

In October, a music-industry executive noted: "People who really want to steal music are going to steal it. You're just making it hard for people who want to do the right thing to get the music they legitimately purchased on the devices and services that they want."