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Web content filter - how it works

This page is intended to point out some of the important features of and to dispel some of the myths surrounding the Web content filtering software now in use within the University.

• The filter works by comparing requested URLs against several lists of "blacklisted addresses". If the requested URL matches an entry in one of the lists, the content of the URL is replaced by this page. Thus the term blocked is not strictly correct, replaced would be more accurate.
• If your browser cannot retrieve the contents of a particular Web page, that is, nothing is displayed at all, this is not because the URL is being blocked. The cause will lie elsewhere; the associated Web server or its connecting network may be out of service. Remember a blocked URL's contents will be replaced, not blocked.
• The lists of "blacklisted addressess" are assembled by a "robot" program in much the same way as the major search engines build their databases. The "robot" is not run by the University but is operated by the providers of the filter software. At intervals staff within DISS download updated "blacklists" from the provider and install them locally. The blacklists contain either domain names (not actual Web sites, of which more later) or complete URLs. The blacklisted items are categorized in extremely broad terms. They do not reach the detail level that could identify individual lifestyle groups or political affiliation, for example.
• The local administrator can decide which categories should be blocked or not (because of the broadness of the categories supplied, almost all are configured to be blocked).
• If a particular URL or Web site is blocked and that site is associated with a particular lifestyle, political affiliation, gender, race, colour or other social grouping, it does not imply that all related sites will be blocked and it does not imply that the University has made any decision to impose restrictions on that group. It simply means that a particular URL is listed in one of the blacklist files used by the Web filter software.
• Mentioned above is the fact that the blacklists contain, not full Web site addresses (e.g www.xxxx.com) but only the domain name of the site (that is the portion of the name with the www removed). Any site within that domain will be blocked by the filter. This can lead to some common sites being blocked inadvertantly. This is likely to occur with domains that host several "undesirable" Web sites. The "robot" will elect to put the entire domain into its blacklist collection.
• There is no intention to restrict access to the Web for genuine research or teaching reasons. Any URL or domain may be removed from the blocked list on demand, so long as it does not contravene the Conditions for using IT Facilities.