Researchers have unveiled a study at the RSA security conference that concludes Windows is more secure than Linux.
Richard Ford, a computer-science professor at the Florida Institute of Technology and Herbert Thompson, director of security research and training at Security Innovation, claim that Red Hat's Linux is vulnerable for more than twice as long as Windows.
Servers running Windows Server 2003 and Red Hat Enterprise Server 3 were tested for security with databases, scripting engines and Web servers.
They took into account the number and severity of vulnerabilities as well as the response time of Microsoft and Red Hat in issuing patches to fix any issues.
That said, anybody in the computer security business wll tell you that ther is no such thing as a secure computer.

Max security level = machine not connected to network, in room by itself and switched off!

OR

Max security level = machine running Xpor 1.62 "Dreamchild", connected to internet, and as far away from Chris Dockree as possible.