Legally Decrypt iTunes Purchased Songs

Every song purchased from the iTunes Store comes encrpted with what Apple is calling FairPlay which resricts the amount of computers you can hear the downloaded songs on, requiring your apple ID and Password for each.

The hymn (hear your music anywhere) project allows it's users to unprotect or unlock music files that are downloaded via iTunes music store.
The following was taken directly from http://hymn-project.org.

The purpose of the Hymn Project is to allow you to exercise your fair-use rights under copyright law. The various software provided on this web site allows you to free your iTunes Music Store purchases (protected AAC / .m4p) from their DRM restrictions with no loss of sound quality. These songs can then be played outside of the iTunes environment, even on operating systems not supported by iTunes and on hardware not supported by Apple.

Why use Hymn Project software?

• To decrypt your iTunes protected AAC files so that they can be played on operating systems for which no official version of iTunes exists, such as Linux.
• To use non-Apple AAC-capable hardware to play your music.
• To eliminate the five computer limit imposed by iTunes.
• To make archival backups of your music.
• As the first step in converting your music from protected AAC to MP3, Ogg, or your other favorite audio file format, for use with your non-iPod portable audio player.
• To demonstrate your belief in the principles of fair-use under copyright law.

For more information visit the official hymn project website.