Search and destroy.
Hacks happen. Don’t pretend it won’t happen to you. Don’t pretend it hasn’t already.
Actively looking for indicators of compromise is a necessary part of today’s IT security practices. Passive defense has been insufficient for a decade. Perimeter defenses are not enough, and even layered defense-in-depth approaches fail eventually. No matter how entrenched you get, the adversary can still get in. Without actively looking for the enemy within, your network can quickly become hostile.