Yes NAT routers have firewalls you'll be invisible over the net but that only covers hackers with port scanners There's so much hostle code imbedded in websites, applications, and media files that you need more protection that just a NAT router The greatest threats come from the websites & media/applications you view and download and anyone who says otherwise is probably not well informed or one of the bad guys A software security package along with your router is a great idea Software firewalls a great because they can alert you to programs trying to access to internet, programs you did'nt expect to access the net like that new screensaver or game you just installed Firewalls, Anti-Virus, Trojan scanners, Application sandboxes, System Process guards, Spywareblockers will all serve to protect you computer and your private data.
/pcuser32