Using WSE 2.0? Get SP2. Dont't know what WSE is? Here is a quick overview from the download page:
WSE 2.0 SP2 simplifies the development and deployment of secure Web services by enabling developers and administrators to more easily apply security policies on Web services running on the .NET Framework. Using WSE, Web services communication can be signed and encrypted using Kerberos tickets, X.509 certificates, username/password credentials, and other custom binary and XML-based security tokens. In addition, an enhanced security model provides a policy-driven foundation for securing Web services across trust domains. WSE also supports the ability to establish a trust-issuing service for retrieval and validation of security tokens, as well as the ability to establish more efficient long-running secure communication via secure conversations.