What is a good free program to block websites?
If your objective is "parental control", Chrome and FF have extensions and add-ons which work pretty well and have some flexibility to allow or restrict sites as you may deem. A smart twelve-year old could defeat them however. I recommend a password protected site logging and screen image saving package for complete control--after all you're trying to protect your child. These programs can also restrict access to Web sites and programs, for example, chat and messaging products or even the entire Web. Spector Pro from Spectorsoft is a very, very good one, but it's not a freebie. I reinforce this by disallowing my kid to have a computer in his room or to have access to any of the computers in our home, when both my wife and I are not around to provide at least some supervision. Where the computer is concerned, my kid has no privacy. There is too much danger.
Using the hosts file is probably the quickest method here. Your router probably also allows you to block domain names, that would be a more secure method of doing it (and it covers the entire network).
If you have a firewall installed, you should be able to block websites in there as well. As Disposable mentioned, OpenDNS will allow you to filter your network traffic. You can implement OpenDNS network-wide in your router's configuration.
K9 web protection
OpenDNS... It's free and works great.
For example, if you want to block facebook.
start menu > run
copy this text and paste
it will open hosts file
now paste this line at the end of the file
127.0.0.1 facebook.com (if single space does not work, leave a tab)
and save the file (ctrl+s).
facebook will be blocked.
you can block any site like this.