Prevent modified client to connect

Hi there,

So I was thinking about security..
My main concern was how you can prevent modified clients to connect to the server.

As far as I know it is possible to reverse engineer a Unity game. Or even simpler, just get the server IP and connect with a custom client...

How can this be prevented? (Im using HLAPI)

Also, does anyone know where http://docs.unity3d.com/ScriptReference/Network.InitializeSecurity.html
is for uNet? Can't find a single thing that improves the security...

Prevent modified client to connect