I have the same problem. My Galaxy s4 started showing me the same "security policy update" notification yesterday as well as another "prevention information" notification telling me "WhatsApp has been forced to stop for an unauthrorized attempt to access system in your device".
Whatsapp seems to be the only app that causes this. It doesn't actually close but it's really annoying.
Does anyone know what's causing this and how it can be solved?