The songs in your iTunes Library may all seem to be essentially the same. They're audio files; why would they be different? But, if you look closely, you'll find out that while many of the songs are the same kind of audio file, others differ in some pretty major ways.

Finding a Song's Filetype

If you have you the Kind column enabled in your iTunes library (to turn it on, click on the View menu -> View Options -> Show Columns (iTunes 12 only) -> Kind), or view a song's file information (Command-I on a Mac, Control-I on a PC), you may notice that some songs have many different kinds of information attached to them.

In the Kind field, some are MPEG audio files, others are purchased, and yet another group is protected. The question is: what do these differences means? Why are some files "purchased" and others "protected"?

The type of file a song is has to do with how it got into your iTunes library. Songs that you rip from CD will show up in iTunes based on your import settings, while songs you buy from the iTunes Store or Amazon or elsewhere may be something else entirely. Here are some of the most common kinds of files you'll find in your iTunes library and what each one means:

• AAC audio file: This is a standard AAC (Advanced Audio Coding) file. Most likely, you created this file by converting an MP3 or ripping the song from CD using iTunes' built-in AAC encoder. AAC is the file format designed to be the successor to MP3.
• Matched AAC audio file: This is a standard AAC audio file, except that it was downloaded to your computer or iOS device from your iCloud account, using iTunes Match.
• MPEG audio file: This is a standard MP3 file, the classic digital audio format. You may have downloaded it from the web or ripped the song from a CD using iTunes' built-in MP3 encoder.

• Protected AAC audio file: A Protected AAC file was the default filetype for songs purchased from the iTunes Store prior to the introduction of the Digital Rights Management (DRM)-free iTunes Plus format in April 2009. "Protected," in this case, means the DRM built into the file restricts it to being used on devices authorized with the Apple ID used by buy the song. This prevents the song from being copied or shared.
• Purchased AAC audio file: A Purchased AAC file is what a Protected AAC file becomes when it's been upgraded to the iTunes Plus format. This file was still purchased at the iTunes Store, but it no longer has the DRM-based copy restrictions. All songs at the iTunes Store sold after April 2009 are in the DRM-free Purchased AAC audio file format.

Can You Share Purchased Music?

Since all music at the iTunes Store is now Purchased AAC, you may be wondering: does this mean that you can start sharing songs bought at iTunes? 

Sure, technically you can. But you probably shouldn't.

Not only is sharing music still illegal (and takes money out of the pockets of the musicians who made the music you love), but there are some things in Protected AAC files that will make it possible for record companies to find out that you were the person illegally sharing the song.

According to TUAW, the Protected AAC/iTunes Plus songs have information embedded in them that identifies the user who bought and shared them by name.

This means that if you share your music and record companies want to track you down and sue for you copyright infringement, it's going to be easier.

So, you should think twice—maybe three times—if you were thinking about sharing songs you've bought from the iTunes Store. If do, you're making it easy to get caught.

 

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