Squid, an Open Source proxy server is really good proxy server i think, since its free, yet it can serve us enough basic and middle needs of proxy server. Mostly, proxy server is used to limit amount of bandwidth that users can reach, by using proxy server we can distribute bandwidth fairly between user. it can also serve caching service. any request and response through that proxy will be saved as in certain amount of cache size. it then, help us to give faster access, because we don’t need to download all the element of web pages directly from the source, instead we can access the cached pages on our proxy server.
Combination from Squid and Squidguard can works even better. Some instances and educational institutions use it to help blocking unwanted internet access completely and in a good way. In my college for example, it use squid as transparent proxy. All web access will be diverted to this proxy, while squidguard is there to block unwanted web address. At first some methods can be done to bypass this Squid + Squidguard resctriction, for example we can use proxy that available in many websites. But last time i tried it can be used again and any website address i entered through the proxy directed to warning page from squid proxy.
Then i find out that it is the use of Squidguard. by visiting documentation section in its website i find regular expression configuration. using this regular expression configuration, we can detect any words and restrict it. the admin must have found common characteristic of web proxy provider that will convert any address entered into “some.php” string passed into our browser. all the admin needs is just to set this regular expression matched with the string.
Well, since the method i use to bypass proxy is really easy method, i can hope for hard way to block it too. gonna find other way to bypass it though. hope this information can help you to understand how squid and squidguard work.