Apple Released major critical updates to iOS and Mac OS X software, fixing issues with their implementation of SSL (Secure Sockets Layer) which could lead to MITM (Man-In-The-Middle) attacks against their users. Updates can be easily applied in the normal way through "Software Update" or can be manually downloaded.
iOS update released 21 February, 2014:
Mac OS X security update released 25 February, 2014:
These updates should be applied immediately. The process is no different from any other update. "Software Update" can be reached by clicking on the apple in the upper left of the screen on OS X, or through the App Store's Updates tab. This major Security Update will require a reboot of the system. The iOS updates can be applied as you normally would as well, either through iTunes, or via your WiFi connection.