I saw Troy Vinson speak on security and vulnerability assessments at MeasureUP.

He went over a bunch of pen testing tools like Metasploit. Anyways, the most interesting thing to me in this talk was the concept of port scanning. If you bombard every possible port at an IP with a packet you will be able to figure out what is open and what is not and that is called port scanning. If port 80 and 443 are open that suggests that there is a web server up and running and if 3389 is open that suggests that remote desktop stuff exists. If you do this fact finding you will come away with a topographical map of what is at a network which will be useful in your sinister malicious nastiness as a hacker. Even more interesting yet, something that really surprised me, is that this sort of let's-see-what's-out-there discovery is illegal in America. I don't see how this is particular different than driving around a bank and taking photos of it and its security guards with a camera (legal), but I do suppose there is only one reason for casing a joint. Obviously, it's not illegal to do a whois lookup on a domain name, but there is at some point a line one may cross in the sand where one is collecting too much publicly available information it seems.