"It's as bad as you could imagine, that's all I can say," Johns Hopkins University cryptography professor, Matthew Green, told Reuters.
Apple recently caught a bug in its software that allowed hackers to infiltrate iOS users' encrypted messages, allowing the hacker to either read or alter them. Apple issued an update this weekend that they claim fixes the problem, but before that, if you and a hacker were on the same unprotected wireless network—say, in a hotel lobby—they would be able to access the said information, even if it were through a protected site like Facebook. The hacker would act as a "man in the middle" and watch the information flow between you and the server. Essentially, the hacker would pretend to be the site that you're logging your information into, whether you're writing a stupid email or making purchases with your debit account—all kinds of bad.
"This sort of subtle bug deep in the code is a nightmare," Adam Langley, a Google employee, wrote. "I believe that it's just a mistake and I feel very bad for whomever might have slipped in an editor and created it."
So, what can you do? Update to iOS 7.0.6 RIGHT NOW. Go to Settings, General, and click Software Update. For all of your iOS devices. Unfortunately, the problem affects OS X for Macs as well, but Apple hasn't released an update yet—so try to stay off public Wi-Fi hotpots.