WebMask is a filter program that removes adverts from web pages. You run it in the background, and tell your browser to retrieve all pages via WebMask. WebMask downloads the pages, except for the adverts, and passes them on to the browser.
It works by not downloading certain images. You specify these with filters, based on the URL. WebMask comes with a comprehensive set of these filters to remove adverts from many popular web pages. You are encouraged to add more.
You can save and load sets of filters. A set of filters for WebMask is maintained on the WebMask web page. You can download new sets periodically, and you can e-mail your own sets of filters to the site for incorporation.