The introduction of Modern UI apps in Windows 8 has added a whole new layer of security in the operating system. Modern UI apps can be installed by standard users. In order to keep the system secure with all this added functionality, Microsoft created a sandbox architecture that is primarily used for Modern UI apps. Modern UI Apps live in an AppContainer. The AppContainer defines the sandbox and the identity of the App.
Microsoft published very little information about AppContainers. One of the most detailed articles on the Microsoft site is a blog on Enhanced Protected Mode in Internet Explorer by Eric Law [ex-MSFT]. The article was written in the Windows 8 Release Preview time frame and partly contains outdated information about IE10.
Continue reading: Demystifying AppContainers in Windows 8 (Part I)