If you have Windows Phone 8 you might be aware of our strong security stance of offering only digitally signed apps you can download from your phone or from the web in Windows Phone Store.
Now we’ve taken another step to help reduce risk and increase safety with your PC apps. Security updates for Windows 8 apps will be automatically installed as they are ready. This will include updates for programs that come pre-installed for Windows 8 (like Mail) and for apps that you download.
For more information, read the announcement at Microsoft Security Response Center or the official policy page.