WebFilter

WebFilter is one of the first web filtering systems and was written by Axel Boldt. Its original use was to remove commercial advertisements from web pages, but it can also be used for general web filtering. WebFilter is implemented as an extension to the CERN httpd web/proxy server. Filtering is based on a rules file which maps URL patterns to filter scripts. Whenever a URL is requested that matches a pattern, the script for that pattern is executed to filter the contents of the requested URL. WebFilter does provide a powerful system for filtering content before it reaches the web browser, but it does have a few drawbacks:

• The rules file is difficult to configure and it is not easy to apply one set of rules to multiple URLs.
• Filter scripts are executed as separate processes and can therefore be very slow when processing multiple requests.
• HTTP requests sent by web browsers cannot be filtered.
• There is no HTML parsing mechanism provided.