Operating system is the core piece of software which runs on all information systems, such as network devices (routers, firewalls, etc.), web servers, customer desktops, PDAs and so on. And the security of operating systems is one of the fundamental concerns in the security of cyberspace and e-commerce. Issues of operating system security occupy a central role in applied computer science; yet there has been no satisfactory complete solution to the problem of computer security. Many known vulnerabilities discovered so far are rooted from the bugs or deficiency in operating systems.