A virtual machine is, in most respects, the equivalent of a physical server. Employ the same security measures in virtual machines that you do for physical systems.

For example, ensure that antivirus, anti-spy ware, intrusion detection, and other protection are enabled for every virtual machine in your virtual infrastructure. Keep all security measures up-to-date, including applying appropriate patches. It is especially important to keep track of updates for dormant virtual machines that are powered off, because it can be easy to overlook them.