You have two MP3 files on your computer. One MP3 file is Taylor Swift’s “We Are Never Ever Getting Back Together”. The second MP3 file is “Tidal Wave”, by the Cool Dudes. The "Cool Dudes" is the name of your garage band.

You burn these two songs onto a CD. You listen to this CD in your car and on the CD player in your room. “Fair use” covers you, as you purchased the Taylor Swift song from iTunes.  And the other song, “Tidal Wave”, is one you wrote, yourself, and recorded with your band.

If you burn these two songs onto CDs and give them to friends, you would breach Taylor Swift’s copyright. However, since you wrote and performed on the recording by the “Cool Dudes”, that copyright would not be breached. It belongs to you.

The difference is clear. Two digital files: one created by Taylor Swift – one written by you and recorded by your band. You have the right to share the song you wrote and recorded. But you do not have the right to copy and share songs by Taylor Swift. See the difference?

The same is true with software. If you share a software application you created, there is no infringement violation. The work/application is your own – to share as you wish. However, if you share a purchased copy of Microsoft Office 2010 or Call of Duty: Black Ops, you would be guilty of copyright infringement, as you did not create these items.