Slate describes it as follows:
On Friday night (Feb. 21, 2014), Apple announced a major security flaw in their software for mobile devices. And I do mean major—it left users open to a “man in the middle attack”. That’s pretty bad. If you used an insecure WiFi connection (at a coffeehouse, hotel, or airport, etc.), this flaw could allow someone to interject themselves electronically into transactions you make on your iPhone or iPad, allowing them to access a lot of your information you thought was secure (like, say, credit card numbers).If you haven't updated yet, you should.
