It's a complete fallacy that you can't hack an iphone unless it's been jailbroken.
If someone knows your mobile number, email address and password....essentially all your iphone/itunes details, they can login to your account from another device and use that device as if they were you.
I woke up this morning to 5 alerts on my iphone telling me that an iPad that does not belong to me was now using my phone number, my email address, my icloud, my iMessage and my SMS Message, on their device.
This means that this person now has access to EVERYTHING on my current iphone and in itunes, they can download expensive apps etc, see the messages I send and send messages on my behalf.
I am currently going through the process of changing passwords etc, but I don't think I can get my details back from their iPad...they will still have access to the stuff they've already downloaded (banking apps etc...as long as they don't know my password to that I should be ok though).
Apple is not hackproof.