We all know about the Exynos exploit, a serious bug in Samsung’s kernels that allowed regular apps to gain root privilege. Samsung has fixed the bug, but updates have been slow to roll out in the US. T-Mobile is getting theirs out now for the Note II, and if you’re running stock firmware, you can download it now.
It’s very important that you perform the upgrade. The bug is serious and could both damage your phone and expose sensitive information. Plus you’ll be getting other various bug fixes. So go to Settings > About phone > Software update and check for new updates.