Security hardening for VMWare ESX Server 3.x - Part 1

With the proliferation of virtaulization in the enterprise one of the questions that is on most administrators minds is; how secure is my virtual environment?

VMWare's ESX Server has a built in firewall and the virtual switching prevents systems from communicating across VLAN boundaries but what about the ESX server itself or the VMWare tools application that is inevitability installed within each guest OS. We could take the approach that the ESX server is hardened out of the box and that nothing more is required to secure our virtual environment however that assumption would leave the virtual infrastructure subject to various attacks that could impact a wide range of network services.