Link: AppArmor - Ubuntu Wiki.
I suppose it was inevitable. As more users come to the Ubuntu Linux fold, hackers and badsters are invading the formerly pristine Linux wilderness looking for security holes. Linux, by its nature, is more secure than Windows; many operations require password access. However, Linux isn't perfect, and Dan Covington, of Kansas Business Attorney alerted me to the fact that Ubuntu Linux reads certain password files that most users would rather be kept private. Enter AppArmor, which is a security extension for Ubuntu Linux. Security is for everyone.