Currently there are more than 40 million web sites and tens of thousands of adult web sites, with new adult sites being added everyday. Moreover, current adult web sites often change their addresses. Most developers are fully aware that it is essentially impossible to keep track of them all. In order to limit this material a number of filter programs have been developed. Most of these programs provide a useful but limited block to adult sites.
Filter programs rely on a database of known adult sites.
It is estimated that their are more than 50,000 adult sites with many more web pages. However, web filters are usually limited to restricting less than 5 percent of these sites. Thus, they focus on limiting the most popular or well known sites. Moreover, hundreds of new adult sites are added weekly. Filters are unable to block sites that are new.