A physical definition of security will not protect you. UCSD's Shimomura defines securing network systems in the language of war. We have to change the way we think about the problem. We must change from using passive techniques to confrontational ones. We must engage our opponent, rather than wait for the opponent to come to us.
Traditional security is passive, and it's atomic.
Security must be aggressive. It must also be systemic. It must be focused on protecting the information, the contents of the system, not the device itself. That focus changes the rules. Securing your network is more than simply patching in products that verify identities or encrypt data passing on the wire.