Perhaps because of limitations on the number of human reviewers and because of the large number of new pages that are added to the Web every day, filtering companies also widely engage in the practice of categorizing entire Web sites at the “root URL,” rather than engaging in a more fine-grained analysis of the individual pages within a Web site.  For example, the filtering software companies deposed in this case all categorize the entire Playboy Web site as Adult, Sexually Explicit, or Pornography.  They do not differentiate between pages within the site containing sexually explicit images or text, and for example, pages containing no sexually explicit content, such as the text of interviews of celebrities or politicians.  If the “root” or “top-level” URL of a Web site is given a category tag, then access to all content on that Web site will be blocked if the assigned category is enabled by a customer.  In some cases, whole Web sites are blocked because the filtering companies focus only on the content of the home page that is accessed by entering the root URL.  Entire Web sites containing multiple Web pages are commonly categorized without human review of each individual page on that site.  Web sites that may contain multiple Web pages and that require authentication or payment for access are commonly categorized based solely on a human reviewer’s evaluation of the pages that may be viewed prior to reaching the authentication or payment page.

Because there may be hundreds or thousands of pages under a root URL, filtering companies make it their primary mission to categorize the root URL, and categorize subsidiary pages if the need arises or if there is time.  This form of overblocking is called “inheritance,” because lower-level pages inherit the categorization of the root URL without regard to their specific content.  In some cases, “reverse inheritance” also occurs, i.e., parent sites inherit the classification of pages in a lower level of the site.  This might happen when pages with sexual content appear in a Web site that is devoted primarily to non-sexual content.  For example, N2H2’s Bess filtering product classifies every page in the Salon.com Web site, which contains a wide range of news and cultural commentary, as “Sex, Profanity,” based on the fact that the site includes a regular column that deals with sexual issues.  Blocking by both domain name and Ip address is another practice in which filtering companies engage that is a function both of the architecture of the Web and of the exigencies of dealing with the rapidly expanding number of Web pages.  The category lists maintained by filtering software companies can include URLs in either their human-readable domain name address form, their numeric Ip address form, or both.  Through “virtual hosting” services, hundreds of thousands of Web sites with distinct domain names may share a single numeric Ip address.  To the extent that filtering companies block the Ip addresses of virtual hosting services, they will necessarily block a substantial amount of content without reviewing it, and will likely overblock a substantial amount of content.