Apple:
The OS X Mountain Lion v10.8.5 Update is recommended for all OS X Mountain Lion users. It improves the stability, compatibility, and security of your Mac. This update:
Fixes an issue that may prevent Mail from displaying messages
Improves AFP file transfer performance over 802.11ac Wi-Fi
Resolves an issue that may prevent a screen saver from starting automatically
Improves Xsan reliability
Improves reliability when transferring large files over Ethernet
Improves performance when authenticating to an Open Directory server
Addresses an issue that prevented a smart card from unlocking preference panes in System Preferences
Contains the improvements included in MacBook Air (Mid 2013) Software Update 1.0
Check Software Update now for the update.