The patch is related to a bug in the Windows Font Driver, which could lead to someone’s machine being hijacked remotely.
Microsoft said it hasn’t encountered attacks based on the bug, but has warned users of Windows to download it if they don’t have automatic updates switched on.
The list of affected systems is so long that you can assume you will need to install it, whether you’re using Windows RT, Windows 7, Windows Server 2008 and even Windows Vista.
Microsoft acknowledged the help of third party security companies who participate in coordinated vulnerability checking. You can find more details of the bug at the Microsoft technical page, here.