A Definition of Network Security

The following defintion of network security is Jesper M. Johansson and Steve Riley's view from Protect Your Windows Network : From Perimeter to Data.

Network security is a process, a task description, not an end state. Therefore, we like to talk about network protection as the goal, and network security as a task description. The task is to detect problems and, preferably before someone else does, respond to those problems in a way that prevents them from becoming security vulnerabilities. At that point, the process repeats, and we look for more problems to prevent.