http://www.bigantsoft.com/tutorial/Advantages-and-Disadvantages-of-an-Instant-Messenger.html

==========================It provides end-to-end security. Because message security directly encrypts and signs the message, having intermediaries does not break the security.It allows partial or selective message encryption and signing, thus improving overall application performance.Message security is transport-independent and can be used with any transport protocol.It supports a wide set of credentials and claims, including issue token, which enables federated security.Using message security has following disadvantages: ========================This option may reduce performance compared to transport security because each individual message is encrypted and signed.It does not support interoperability with older ASP.NET Web Services (ASMX) clients because it requires both the client and service to support WS-Security specifications.