The OS X Mountain Lion v10.8.4 Update is recommended for all OS X Mountain Lion users and includes new features and fixes.

Updating your system

1. You should back up your system before installation. To do this you can use Time Machine.
2. Do not interrupt the installation process once you have started to update your system.
3. You may experience unexpected results if you have third-party system software modifications installed, or if you've modified the operating system through other means.
4. Click the Apple () menu and choose Software Update to check for the latest Apple software via the Mac App Store, including this update.
5. Other software updates available for your computer may appear, which you should install. Note that an update's size may vary from computer to computer when installed using Software Update. Also, some updates must be installed prior to others.

You can also download the manual update installer. This is a useful option when you need to update multiple computers but only want to download the update once. These versions of the standalone installers are available from Apple Support Downloads. 

About the update

The OS X Mountain Lion v10.8.4 Update is recommended for all OS X Mountain Lion users and includes features and fixes that improve the stability, compatibility, and security of your Mac, including the following:

• Compatibility improvements when connecting to certain enterprise Wi-Fi networks
• Microsoft Exchange compatibility improvements in Calendar
• A fix for an issue that prevented FaceTime calls to non-U.S. phone numbers
• A fix for an issue that may prevent scheduled sleep after using Boot Camp
• Improves VoiceOver compatibility with text in PDF documents
• Includes Safari 6.0.5, which improves stability for some websites with chat features and games
• A fix for an issue that may cause iMessages to display out of order in Messages
• Resolves an issue in which Calendars Birthdays may appear incorrectly in certain time zones
• A fix for an issue that may prevent the desktop background picture from being preserved after restart
• A fix for an issue that may prevent documents from being saved to a server using SMB
• Addresses an issue that may prevent certain files from opening after copied to a volume named “Home"
• A fix for an issue that may prevent changes to files made over NFS from displaying
• Resolves an issue saving files to an Xsan volume from certain applications
• Improves Active Directory log-in performance, especially for cached accounts or when using a .local domain
• Improves OpenDirectory data replication
• Improves 802.1X compatibility with ActiveDirectory networks
• Improves compatibility when using mobile accounts