There are a number of ways to deal with unhandled exceptions in ASP.NET MVC.  By default, nothing is handled and users are shown ugly error stack traces.  With a bit of effort, and using some of the same configuration values that have always been available within ASP.NET, it is easy to set up much friendlier error pages.  If you need to be able to really customize the way errors are handled, you can override the HandleError attribute, or you can create a custom ViewResult that encapsulates the details of the exception and specifies how they should be displayed.

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