Dude ... Your question is too broad !. It's sorta like asking how a burglar breaks into a house.
There are hundreds of ways you can think of. Try googling !!

He may or may not use tools developed by him !. It Depends on what he's hacking and the
amount of spare time he has.


Any Pc thats connected to the internet; be it a server or be it an ordinary box , should run a
firewall. There are a lot of freely available firewalls around. Just google for em !!


Yeah.. like sec_ware said..... Nessus,Satan etc. gives an account of the vulnerabilities.

Downloading Updates and Patches, running a good firewall are some of the ways to keep your
box safe. A lot of people don't give a damn about physical security. Cutting the cables of the
network is easier than ip spoofing or a dos attack !!.


So stay safe .. And don't practice Security by Obscurity !