Researchers recently found an issue with how both iOS and Mac OS X Mavericks handle SSL/TLS transactions. This is used to encrypt data over the Internet, usually through web browsers like Safari. How would this affect you? It could put your private information at risk of being intercepted by a third party. An example of that information would be your credit card number. Thankfully, after four days of being ‘exposed’, Apple has released an update that corrects this vulnerability. You can obtain it via Software Update (go to the Apple menu in the upper left corner of your screen and select Software Update). Run the update to 10.9.2. This will require a restart, so save any work you have open.
More information about the exploit and the fix can be found here.