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.
Directorate of Information Technology