Content filtering on the internet has become more and more common. As a matter of fact, some governments such as Saudi Arabia, Pakistan, China and Iran have put into place Internet-censorship laws that have extended the censorship to almost each and every locally-available site. This is also quite popular in a number of institutions especially schools and offices. Each institution has its reason for blocking websites. In most cases, they do not want their students or employees to waste time on ‘useless’ sites. The most commonly-blocked sites include social sites, Yahoo!, YouTube, MySpace, Orkut, StumbleUpon, Facebook, Twitter and the like.