http://news.cnet.com/8301-1009_3-576...law-very-soon/
A security hole has been found in iOS and OSX, which allows a hacker to access personal data (including credit card numbers) while you're accessing a public network.
If you have an iPhone or an iPad, Apple has an update out that fixes the issue. So it's best to immediately update if you have an iPhone/iPad.
Macs don't have an update yet, but Apple says that it should be out "very soon". Considering the severity of the hole and the fact that it seems incredibly simple to fix, my guess would be that it will be out in the next couple days.
Until then, avoid public wifi if you use a Mac.