The OS X Mavericks 10.9.3 Update is recommended for all Mavericks users. It improves the stability, compatibility, and security of your Mac.
– Improves 4K display support on Mac Pro (Late 2013) and MacBook Pro with 15-inch Retina Display (Late 2013)
– Adds the ability to sync contacts and calendars between a Mac and iOS device using a USB connection
– Improves the reliability of VPN connections using IPsec
– Includes Safari 7.0.3
For detailed information about this update, please visit: http://support.apple.com/kb/HT6228
For detailed information about the security content of this update, please visit: http://support.apple.com/kb/HT1222