Some stand-alone systems allow installers to remove selected websites themselves. However, user discretion is limited in this regard. List-based blocking either blocks certain sites that have been explicitly listed or allows only those cites that have been explicitly listed. Filter vendors search for and identify the sites that meet certain criteria. These lists make up the list of websites that are either blocked or allowed.
Some software allows users to configure the filtering criteria to a great extent.
Users may make a selection from a list of the categories of the types of websites that they would like to block. Websites containing objectionable words or phrases will be blocked. The PICS standard enables users to electronically distribute descriptions of digital work in a simple, computer-readable form. The use of PICS allows computers to analyze these labels and automatically shield users from certain material or for identifying websites of interest. The PICS system is based on a distributed listing of ratings.