How to Block Specific Web Sites Using AD / Group Policy

I am not having success blocking the web proxy site called kproxy.com. I did try to block by URL, all of the 17 IP addresses, etc. Is there anything that I can do within Group Policy to block that site and all of its 17 web servers? It might be something related to a hosts file which might be applied to all computers. Any ideas?

Instead of what you are doing, the best way is to usually include doing this at the Firewall/Proxy Server. Internet Security and Acceleration server is a the microsoft proxy server and you can even vary this by user account and group membership.