I try to block sites in squid based on this article. Assuming you would want to block access to Yahoo (e.g http://www.yahoo.co.jp, http://www.yahoo.com, http://www.yahoo.co.in), you would ideally want to block all of the above URLs, if I use a regular expression and try to search something called yahoo it seems to get blocked.

We are just interested in applying rules which would be most commonly used across all companies (e.g. social networking sites like facebook, orkut), porn sites (e.g. sex), gaming sites (games), movie & song download sites, and sites where they can upload data (e.g. rapidshare)

What would be the common set of effective rules in achieving the above?