There is no way to prevent this. But, but this not what ouyou should worry about. What you need to worry about are the guys scanning your networks, patiently building knowledge on cracks in your network.
What you need to do is to Preventprevent exploitation, use a very strict access control, bring in pen tester, find things that are misconfigured, understand perfectly your network, and train people (not to click on well crafted emails, nonot to go on weird web sitesites, be cautious about removable devices, etc.).