Your smartphone can vulnerable if you put on some unnecessary settings you don't need. Hackers/Advertising agent can slowly get information about you and use it against you. I will show you different ways to help yourself from hackers on your iPhone device.
Change your passcode : A lot of iPhone users are fond of the 4 numbers passcode. The first thing you want to do is change the passcode to something with letters and numbers.
Go to settings on your iPhone, select passcode, enter your passcode. Then you will see simple passcode, change it from the simple passcode to something more complex. Turn off simple passcode and use something else..mix it up with letters and numbers
And stop using your birthday year as passcode 
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Limit Advertisment tracking: Limit the advertisement you receive on your iPhone. Advertisers can can get who you are via your tracking ID and with your information on iPhone to know who you are. To prevent this. Limit tracking ID on your iPhone.
Also reset your Advertising identifier. This will help shows advertisers that this is a different person from yesterday, so it will be difficult for advertisers to gather enough information to track you. Always reset your Advertising ID periodically.
Go to Settings----> Privacy--->Advertising
Location settings : Go to privacy----> location services---> System services--->Frequent locations. This will show a list of all the locations you have been through. The addresses of each location you have visited in the past, the time you spent at this location. You can turn this on or off.
Turn Off Bluetooth : If you are not using your Bluetooth, turn it off. Most people will use their name as the phone name and can let people know who is who in public and might as well be more interested in you
Stay safe online and make sure you are always safe with your iPhone/ipad device.