It may sound clichéd to say that managing security threats inside an enterprise environment isn't like it used to be, but this is the honest truth. It's no longer a question of whether portions of your environment are compromised, but rather now it is a question of when you will figure it out.
In other words, most security professionals currently take the posture that assets within their control have already been compromised and that active measures must be taken on a daily basis to find any occurrences of these Indicators of Compromise (IoC).
This is not to say that you should give up on perimeter security because the effort is moot; security teams still need a solid set of rules and policies that will safeguard internal assets from the outside threats that are trying to get into an environment. Firewalls and other...
