Updated Apple has today emitted security updates for pretty much everything it makes, and you should install them as soon as you can because it's all bad news.
The details are pretty boring to anyone who isn't a security geek like me, but these are pretty serious. Let's get patching.iPhones, iPads and iPods should grab iOS 9.3, Macs should fetch OS X 10.11.4 or Security Update 2016-002 for non-El Capitan Macs, Apple Watches should get watchOS 2.2, and Apple TVs should install tvOS 9.2. Your hardware should eventually offer the updates to you automatically, or you can follow these instructions to get going right away.
UPDATE 25 March 2016 09:27: If you have an iPad, DO NOT update it with this patch. It seems that the patch has been bricking iPads left and right. Apple says it's working on a fix.