Even Microsoft's lawyers say it: Windows RT isn't Windows. In fact, Microsoft is releasing two different operating systems: Windows 8 and Windows RT (Run Time). While the two versions look alike on the Metro layer, Windows RT stands apart for two reasons: It runs only on ARM-based systems such as Microsoft Surface, and the traditional Windows desktop is gone, which means the only non-Metro applications that work with Windows RT come with the OS.
The differences between Windows 8 and Windows RT carry over to computer security. Some Windows RT characteristics decrease security risk, but there are missing features as well.