in OSs and programming. A attacker can invade a certain network at a chance but Security Experts must can prevent any kinds of attacks. When I was working as a Unix network administrator, my friend, a talent university guy, invaded my Internet PPP server by using a software loaded from Internet although he knew nothing of Unix at that time. In my opinion a practicable way is to train yourself to be a real Security Expert which requires a excellent network environment to practice and your talent. Checkpoint and Cisco Firewall are nothing because they give you a friendly user interface to implement the rules. If your English is excellent and expecting a good luck in your future job seeking you can try the easy way.