Don’t Want to Update your Mac to OS X Yosemite? Hide the Update from the App Store
While many Mac users have updated to OS X Yosemite, a notable amount have chosen to stay on OS X Mavericks or Mountain Lion for a variety of reasons, and some have even had to downgrade due to frustrations or incompatibilities that were experienced with the new version of OS X. Whatever the reason, if you’re wanting to stick on a previous version of OS X that you are happy with, you should probably hide the Yosemite update so that you don’t accidentally install it.