With the increasing number of cyber threats, no enterprise is safe from attack. Prevention, while an important and necessary component of your overall security posture - and while quite effective against "commodity" attacks - does not provide sufficient protection in today's dynamic, targeted threat environment.
In short, "putting all your eggs in the prevention basket" is a losing proposition. You must be able to detect and respond to attacks that penetrate the perimeter quickly and resolve them before they do irreparable harm to your organisation and your customers.
