i study in a college and thus naturally behind a proxy server that has a firewall which blocks all urls containing certain strings such as mp3,chat.........and so on.......

But we can access all these urls by just appending them with ?java
For example: http://www.***mp3***.com will give an access denied message but
http://www.***mp3***.com?java will simply open the site as if it was just any other site.

Why does this happen?