Can you tell me the make and model of your phone please?
Ok, I can help you with the iPhone 5.
Has someone had access to this phone for a any amount of time?
Ok, at the moment I'm just waiting for an answer to my question.
in order to "hack" your iPhone a person must have direct, lengthy access to the device. If you do not think this is likely then the iPhone should not be effected.
You can prevent tampering by enabling a passcode for the iPhone.
To change your passcode or passcode settings, go to Settings > Passcode. You'll find several settings and options.
Turn Passcode on if it is not already. Enter your passcode, confirm it and activate it.
If you are unsure if someone has had access to the iPhone or just to be safe. You can back it up and restore it to remove any possible malicious software. If you'd like those directions, please let me know.