If you have a computer running Mac OS X, chances are you have downloaded files from the Apple support web site. You can actually verify the integrity of these support files using a simple script.
You have two options on how to update your Mac OS X. The first option is using the Software Update program accessible via the Apple icon. The second option is by downloading the updates via the Apple Support download site. I have actually resorted to the second option a number of times because of errors I get using the Software Update program.