Security is always a top consideration for an information technology (IT) infrastructure. The security weakness in a virtualized IT infrastructure can pass the vulnerability to virtual machines (VMs) or even the physical computers. In addition to these general security measures, the vSphere virtualized computing environment has its own specific security measures. To make the VMware computing environment secure, VMware vCloud Suite provides many security features such as firewalls, user authentication, and server certification. While considering how to secure the vSphere virtual environment, this chapter focuses on the subjects related to the user authentication and authorization, and certification. A virtual network may include elements such as virtual local area network (VLAN), virtual network adapters, virtual switches, distributed virtual switches, ports, and port groups. A firewall is provided to protect virtual networks at different levels. The firewall can be configured to make the network traffic go through certain ports, block certain protocols, or block the traffic coming from certain hardware addresses.