Updating iTunes Says It Will Change My Hard Drive
This happens when a application (like iTunes) or other try to modify your hard drive and install files on it, but your settings are such to prevent that.

It is advisable to set that alert so to prevent applications installing without your explicit approval.

The settings are in the system preferences - Security &amp; Privacy - general tab.

Here you can set your choice what happens when a new Application tries to Install it self.