There is a major flaw in Apple's software for mobile devices that could allow hackers to intercept emails that are meant to be encrypted.
The issue is a "fundamental bug in Apple's SSL implementation." All Apple users are recommended to update their iPhones operating off of the iOS7 to the latest patch that is now available, 7.0.6.
To update your iPhone to the latest patch, go to Settings > General > Software Update. Download and install iOS 7.0.6.
More information available here: http://support.apple.com/kb/HT6147