This document discusses security challenges and opportunities in virtualized computing environments like cloud computing. It begins by defining key concepts like hypervisors, virtual machines, and security layers. It then explores how traditional network security approaches need to be adapted to the virtual environment. Specifically, it examines how firewalls, intrusion detection/prevention, anti-virus, encryption, and patch management can be implemented as shared security services across virtual machines. The document also discusses challenges around data privacy, incident response, compliance, and service management in virtual environments and how "Security as a Service" approaches could help address some of these issues. In the end, it argues that many security problems posed by virtualization can be solved through adapted traditional methods and emerging standards