virtual system. This as you say that in future advanced firewall and security would hamper bitcoin from invaders / hacked .
however blockchain there is to add protection and multiple layers with a secret key .
A firewall is not going to stop something that anyone can attempt to crack locally. Regarding Keys.
If you are on about nodes. then for them to accept connections on the p2p port it would have to be open anyway, so a firewall doesn't help in this situation either unless you block down exactly who can use your full node, which makes no sense anyway. firewalls can already do this kind of stuff.