For more information, see the following resources:
"Security in .NET: The Security Infrastructure of the CLR Provides Evidence, Policy, Permissions, and Enforcement Services" by Don Box, MSDN Magazine, September 2002, at http://msdn.microsoft.com/msdnmag .
"Security in .NET: Enforce Code Access Rights with the Common Language Runtime" by Keith Brown, MSDN Magazine, February 2001, at http://msdn.microsoft.com/msdnmag .
.NET Framework Security by LaMacchia, Lange, Lyons, Martin and Price, published by Addison Wesley.