Yesterday Apple released security updates for Apple Safari, OS X Yosemite (10.10), OS X Mavericks (10.9) and OS X Mountain Lion (10.8), Apple iPad (2nd generation and later), Apple iPhone (4S and later), Apple iPod (iPod Touch 5th generation and later), Apple TV (3rd generation and later), Apple Safari and finally Xcode for OS X Mavericks and later.
Full details on all updates are available on Apple’s Security Updates page. The updates to prioritize in my opinion are the updates for:
Apple TV:includes fixes for WebKit
Apple iOS: includes fixes for WebKit, the iOS kernel and 2 lockscreen bypasses
OS X (10.10, 10.9 and 10.8): includes fixes for Apache, OS X kernel, NTP, OpenSSL and PHP
Apple Safari: since it address 5 critical memory corruption flaws (as well as 5 other CVEs)
If you use any of the above software, please install the appropriate updates as soon as possible. As a routine precaution I would recommend backing up the data on any device for which you are installing updates in order to prevent data loss in the rare event that any update causes unexpected issues. Thank you.