How do stand-alone programs determine what should be blocked?
Currently available filtering tools use some combination of two approaches to evaluate content: lists of unacceptable (or acceptable) sites, and keyword searches. List-based blocking works by explicitly enumerating sites that should either be blocked or allowed. These lists are generally provided by filter vendors, who search for sites that meet criteria for being classified as either “objectionable” or “family-friendly”. Filtering software vendors vary greatly in the amount of information and control they make available to users. Most vendors do not allow users to see the actual list of blocked sites, as it is considered to be a kind of trade secret. However, some vendors provide detailed descriptions of the criteria used to determine which sites should be blocked. Some vendors might allow users to add sites to the list, either in their own software or by sending sites to the vendor for review. Stand-alone filtering tools also vary in the extent to which they can be configured by user
