You may recall my post earlier this week about the security flaw that was discovered in Mac operating systems. Apple issued a patch to fix the flaws for iPads and iPhones and now they have issued a fix for Mac computers too.
The security fix is embedded in a general upgrade to v.10.9.2 and you can get it by going to the Apple menu and selecting Software Update.
The upgrade adds some new features and functionality and fixes some other bugs as well. You can read about what v.10.9.2 does here.