I have an iPhone 7 with iOS 10.2.1 on the Sprint network. I was texting a friend about paczki (Polish donuts). 15 minutes later, a random number from Jamaica NY sent me a picture of paczki. The only thing I can think of is that this person is looking at my phone and read my messages. How can someone access my phone in this way and how do I secure my phone from this? Thank you in advance for any help.