Weird OSX behavior

[xplan303ex]

After the last security update for OSX 10.3.9 (released today), I was asked to update my keychain access, so I told the computer to change all, it did but I lost the preferences of all my applications, my iTunes library was gone (I had to re import all the music files again - gladly they weren't gone), I lost my Safari bookmarks, my IM program preferences, etc etc.

What caused this to happen? How can I prevent it from happening again?

 

[slur]

I've heard of such problems. Before performing any upgrade, it's a good idea to run a full repair on your disks while booted from an installer CD, repair permissions afterwards, back up your home folder and your critical data, most especially ~/Library/Preferences and Application Support. Disconnect all excess firewire and USB peripherals from your computer. Turn off any non-essential Login Items. Quit all applications before doing any system update.

I also recommend you download the update and run it from your hard drive instead of running it within Software Update.

It's also not a bad idea when doing system updates to *always* use the Combo Updater. Since 10.3 Combo Updaters can be run on any minor system version up to and *including* their own they can be used to ensure things are as complete as they should be, when the system acts up.

That's as much as you can do. If problems occur regardless of all these precautions, you at least have your backup as a last resort.