The security content of the VI3 courses (VI3 DSA, VI3 Fast Track) was mostly focused on locking down the Service Console, because it was developed before the launch of ESXi. Of course, now that ESXi is here, there's a better way to lock down your Service Console: don't have one.

In 2010, we plan to release a vSphere 4.x-based virtualization security course. It'll cover all aspects of the security of a vSphere/vCenter deployment.

In the meantime, certain third-party providers are offering their own independent vSphere security courses. I have no information about the quality of these courses: some could be great, some could be terrible.