Good article on how to protect yourself on the net.
If you’re smart and you’re connected to the net, you’re concerned about computer security. Open ports on your computers are invitations to criminal hackers and other evildoers to wreak havoc – and if you don’t protect yourself, no one else will. Your ISP and the cops have better things to do than chase hackers from Belarus who deleted the cosplay photos of you in your beard and Sailor Moon schoolgirl outfit. (That’s right, I know about that whole sordid affair).The good news is that much like home security, it’s quite easy to lock the door. Test out those locks with a port scanner utility, which probes your computers for security holes.
The rest of the article goes through NMAP and some cygwin scripts that can help you plug some security holes.