UPDATE 15:20 08/12/10:

MasterCard has now confirmed that they have an issue with their SecureCode service.

From MasterCard:

Please be advised that MasterCard SecureCode Support has detected a service disruption to the MasterCard Directory Server. The Directory Server service has been failed over to a secondary site however customers may still be experiencing intermittent connectivity issues. More information on the estimated time of recovery will be shared in due course.