Make sure MySQL is not accepting remote connections
Do:

netstat -an|grep 3306 | grep LISTEN


If something similar to the following line is returned:

tcp        0      0 0.0.0.0:3306                  0.0.0.0:*                   LISTEN      


.. it means that it's listening on all interfaces.

If something similar to the following line is returned, and no other lines:

tcp        0      0 127.0.0.1:3306               0.0.0.0:*                   LISTEN


.. it's already configured to only listen on localhost.      

If there are lines with other IP addresses before the :3306, it means that it's  listening on those interfaces.

To change MySQL to only listen on localhost, edit your configuration file (usually /etc/my.cnf), add the following:

bind-address = 127.0.0.1


Restart the service and voila!