"Content filtering for the Web can be a messy proposition. A business may need to block only the most objectionable Web sites, while schools may be required by law to follow a more thorough process. Whatever your needs, you can build a solution with only open source pieces: squid, squidGuard, and blacklists.
"The squid server acts as an intermediary between a Web browser and Web server. As a proxy, it receives a URL request from the browser, connects to the server on behalf of the browser, downloads content, then provides it to the browser. It also saves the content to disk so it can provide it more quickly to another browser if the same URL is requested in the near future. Generally, this leads to more efficient utilization of an Internet connection and faster response times for Web browsers..."
