Before revision: Prior to March 2009, digital music files with digital rights management were available for purchase from the iTunes Store, encoded in a proprietary derivative of the AAC format that used Apple's FairPlay DRM system.
After revision: (DRM)Prior to March 2009, digital music files with digital rights management were available for purchase from the iTunes Store, encoded in a proprietary derivative of the AAC format that used Apple's FairPlay DRM system.