How can I prevent Desktop Users from accessing any online website in Ubuntu? I tried
127.0.0.1 * in /etc/hosts but it didn't do the trick.
Please note that I need to keep
http://localhost fully functional.
iptables -A output -p tcp --dport 80 ! --destination 127.0.0.1 -j DROP
as suggested by @hlovdal.
Actually i think both options are very crippling to the system... Is there a reason that we can know why you need the proposed changes? Maybe we can have some easier changes if we know more about your need...
Use IPTables to block all outgoing traffic. https://help.ubuntu.com/community/IptablesHowTo
should block all outgoing web traffic (http requests).