Apple has released 10.9.2 update to fix various vulnerability. After the SSL security issue named as "gotofail" went public last week, Apple has responded quickly and patched that in this update.
There are few new things Mac users are getting in this update such as, FaceTime audio calls, call waiting feature in both FaceTime audio and video calls. It also adds individual sender blocking in iMessages. It has few fixes for Mail and Safari too. For complete listing of security updates and fixes visit the below link. You can get this update through Mac App Store.
http://support.apple.com/kb/DL1725?viewlocale=en_US&locale=en_US