The Security Zone describes the location in which the application is running. Say; for example, a dot-net application that runs through the internet is seen as Internet Zone application. So based on the locations, Dotnet determines the zones and claims a set of securities on it.
This example will help us learn about the Code Access Security and how to apply it to an assembly. The buttons marked as 1 and 2 are used to read the system environment variables called SecTest and UserName. Here, UserName is a built-in environment variable and SecTest is the one we create for checking the Code Access Security. The text box marked as 3 is to display the value to read from the system Env. variable.