So I assume the only two ways to hack a computer are
From the inside out(trojan)
From the outside in(some special program on an open port or exploit)
Now if the firewall blocks all ports and asks the user about each request(and any applications exempt from this have MDsum checking or some sort of confirmation code), than it should be extremely hard to get in, correct? I mean if a trojan is being intercepted by the firewall(do you want to allow etc.), and outside access is blocked, than a user should be safe in most circumstances right?