There is no such thing as a unhackable website. But, there are ways to make it more secure.
Changing the administrator path
One of the problems with Joomla, is the fixed path to the backend administration, which is "/administrator". This is where your login as a content provider or web manager. There is a way to change the path effectively, without having to rename all the references in the source code.
http://forum.joomla.org/viewtopic.php?f=502&t=266026&start=30
