How to remove the installation from centos?

One thing I always do after I install a machine is removing the installation files. Some of this caution may be paranoia, but if you run web services for your company, for example, it's wise to not leave around any obvious signs that someone has been there. A hacker could potentially check if there's an admin user for a service and then use common default passwords to try to break in. 

To remove all traces of the centOS installation. This method removes only centOS, not the partitions and data.