We have recently released an update to the VI3 Security Hardening guide.  The main changes are:

• new content for ESX 3.5 and VirtualCenter 2.5, including VirtualCenter plug-ins
• a section specific to hardening for ESXi.
• new sections for VM configuration as well as client software
• a greater level of depth for the existing recommendations

To keep things simple, the new version uses the same URL as the previous version:
http://www.vmware.com/resources/techresources/726

As always, this and a lot of other security information for VMware products may be found at http://www.vmware.com/security.

Charu Chaubal
Technical Marketing