Thanks Daniel.

So, what´s the best approach to protect wifi?

Same doubt, with an aditional consideration: Supposing there´s no clients (MAC registered) searching for that WiFi, there´s no way to discover the MACs, right? And supposing there´s no SSid announcement, how can someone even detect such network? I think this network, in this scenario, is really invisible. Am I wrong?
So, the guy trying to access that net must have a 24/7 monitoring of a hipotetical network, if he can get the MACs, right.
And then, with a dubbed MAC, what´s next?