Check out this
blog posting about reverse engineering .NET assemblies with Reflector and Relfexil. It shows you a quick password crack by changing the assembly so that all passwords but the correct one are valid. Great if you get stuck with assembiles you can't use in those one off situations. Kinda scary when you actually think about the implications of this.
A buddy of mine just mentioned that the same thing is capable in Java, so its not just an MS thing.