Late last week, Apple released iOS 7.0.6, a bug-fix update to the iOS. Apple releases these small updates all the time, so this didn't seem unusual. However, as people began to understand the bug that the update fixed, it became clear that it was a major security hole.
The bug causes Macs and iOS devices to not correctly check website security certificates. So, anytime you log into a secure site--online banking, e-commerce, etc.--you're potentially at risk. What's really scary is that the bug makes it possible for a hacker to pretend to be your bank or other website and capture your personal and payment information.
Needless to say, you need this update now.
The update is also available for iOS 6 and for the Apple TV. An update for Macs will be released soon, according to Apple.