The article http://lifehacker.com/146448/geek-to-live--ban-time+wasting-web-sites recommends editing the Windows HOSTS file in c:\windows\system32\drivers\etc as a way to block certain websites.
I noticed some interesting behavior when adding the line: 127.0.0.1 google.com.
In Firefox 7.0, when I attempt to navigate to 'google.com', I get a Server Not Found error, as expected. However, when I attempt to navigate to 'www.google.com', the page is retrieved without error.
Why the different behavior? Why does it resolve the URL differently when the www is prepended to the domain name?
Update: With the line edited to '127.0.0.1 google.com www.google.com', both above requests are blocked. I'd still like to understand the reason for the different resolution. I see, using PING, that the URLs in question do resolve to different IPs.