A web filter screens and blocks objectionable web pages by (1) intercepting a user's request to view a web page, (2) determining that the requested page contains objectionable content, and (3) prohibiting the user from accessing that web page.
Web filters can observe and respond to requests in two main ways. One method, pass-through technology, requires the Web filter software to be integrated with other network devices such as proxies or gateways. This ensures that all requests pass through the Web filter to be accepted or denied.
Another method of handling requests, known as pass-by technology, requires the Web filter software to be installed on a stand-alone server and placed on the network of machines that it is to filter. The Web filter then receives all of the traffic that exists on the network, but it does not prevent the network traffic from reaching its intended destination. If a request is made for a restricted Web page, the Web filter will display an error message stating that the user’s access to the Web page was denied. The user’s connection with the website is then closed to prevent the Web server from sending additional information to the user’s computer.