Filtering Content: Online Web Proxy Detection

Posted by Derek Brown
As of late, we have seen a fairly significant number of
customer requests for filters that block access to free online proxy websites.
Those of you who subscribe to our Digital Vaccine service have probably noticed
the influx of filters addressing these requests; I thought you might find it
interesting to understand just how it is that we are able to cover such a wide
swath of websites with a relatively small filter set.

One of the easiest ways to evade URL or IP based
filtering is to use a proxy. A proxy
is third-party server that acts on the requestor's behalf to download content
from the Internet. One method of proxied content delivery that is growing in
popularity is online web proxies or CGI-based
proxies. These services are written in a scripting language, usually PHP or
Perl, and hosted on a public web server. A few of the most popular are PHProxy, CGIProxy, and Glype. Applications such as
these allow users to proxy the download of their content in a point-and-click
fashion instead of having to locate an anonymous proxy server somewhere on the
internet, plug in the server IP address and port into their web browser, and
repeat the process until they find a working one.

Suppose, for example, that the network administrator of
your company thinks you should not be performing any type of searches through
Google; most (continue reading...)