Its an absolute essential, very well written and real-world wise. I think most people go for language books, ignoring such important matters as security.

*Uncovers the steps software architects and developers will need to take in order to plan and build a real-world, secure Web services system *Authors are leading security experts involved in developing the standards for XML and Web services security

.NET provides a powerful framework in which to write secure code but unless you understand how attackers think and how the .NET security systems works your code will be vulnerable.