Versions of Enterprise Library earlier than version 3.1 required that you build the source code. Subsequent versions, including this release of Enterprise Library, include pre-compiled strong-named assemblies for all the source code. The assemblies are signed with a Microsoft strong-naming key that is not included with the source code. This means that you cannot build a compiled version from the source code that uses the same public key. However, you can use your own key pair to create strong-named assemblies. If you believe that you may customize the Enterprise Library source code, you should use the binaries that you compile from the source code and sign with your own key instead of using the pre-compiled binaries signed with the Microsoft key.