This is why: BBC News - Security holes unearthed in Apple's iOS7
"Two security vulnerabilities have been discovered in Apple's new mobile operating system, less than 24 hours after its launch.
One flaw concerns a user's ability to recover their data if a device has been stolen. The much-vaunted "Find my iPhone" feature can be disabled be a thief simply by putting the iPhone or iPad into airplane mode, preventing the device from communicating.
The other flaw is potentially even more serious - allowing users' email and social networking accounts to be hijacked even when the user has locked and password-protected their phone"