Pro Business Applications with Silverlight 5

Cross-Domain Access Policies

By default, the Silverlight runtime limits your application to communicating with services that originate from the domain that the Silverlight application was downloaded from, known as the “site of origin.” This restriction was put in place for security purposes to avoid denial-of-service (DoS), cross-site forgery, and various other attacks.

However, there are perfectly valid requirements for needing to communicate with servers other than the site of origin. For example, you might want to write an application in which your domain services exist in a different location from where the Silverlight application is downloaded, or write an application that communicates with external services such as Amazon's web services ...