The update, which is compatible with 2012 model year Macs only, fixes an undisclosed problem with Keychain. Apple's update comes over a month after Supplemental Update 1.0 was released for all systems running OS X 10.8.2, which brought fixes for Japanese character rendering in Mail, ineffective Safari parental controls and startup issues with computers having over 64GB of RAM.
From the Supplemental Update 2.0 release notes:
About OS X Mountain Lion 10.8.2 Supplemental Update 2.0
This update addresses an issue with Keychain that can affect 2012 Mac systems.
This update is recommended for all Mac systems introduced in 2012.
While merely speculation, the Keychain fix may be associated with a similar problem seen in the OS X 10.8.1 that caused the password management system to become inaccessible for some users. The bug was supposedly patched in the most recent build of OS X 10.8.2, according to that update's published release notes.
The update comes on the heels of rumors that Apple is preparing to seed one of the first beta versions of OS X 10.8.3 to Mac developers and AppleSeed participants. Invites for the beta were sent out prematurely at the end of October, suggesting the newest Mountain Lion test version is nearing completion.
Apple's OS X Mountain Lion 10.8.2 Supplemental Update 2.0 weighs in at 26.65MB and can be downloaded via Software Update or Apple's http://support.apple.com/kb/DL1611?viewlocale=en_US&locale=en_US< ahref="http://support.apple.com/kb/DL1611?viewlocale=en_US&locale=en_US">Support Downloads webpage. Although OS X Mountain Lion v10.8.2 is the only listed system requirement, the update will not work on Macs built before 2012.