link textI could not access the link (blocked in office) but i think this may help you edit your host file
"“WWW” has become the universal standard for the default host. It is just as common to define a site with no host as well. This means that as far as DNS goes www.yahoo.com & yahoo.com are two totally different sites, even though they resolve to the same place. Because of this to effectively block the site, you must also block all hosts. This would usually mean:
127.0.0.1 facebook.com
127.0.0.1 www.facebook.com"
check the link for more details.
Also i you trying to block multiple sites, its better to have a proper software like proxy server or firewalls which can block access to particular sites.