NFC range is very short. Any device connecting via NFC is going to have to be almost in physical contact with your device. You didn’t mention what your kind of phone you have, but a quick look at the only device I have with NFC (a 4.4 KitKat phone), the user has to toggle on NFC using a toggle button in the notification bar “pull down menu” (I’m having one of those moments when I can’t think of the proper name of it). On your device, it may require you to go into your settings to turn it on. Someone can’t just switch NFC on without having physical access to your device. Also, I am fairly certain that NFC is inactive when the screen is off to save battery life on most devices, so they would need to have your device within a few centimeters of their device, NFC must be enabled, and your screen would need to be on. Even then, it isn’t as if NFC grants a free pass to your file system. It essentially operates like a very short range Bluetooth connection, but without the hassle of pairing. There are just too many step to go through for this to be a likely method for someone to steal information off of your device. I’m not sure of a way that you could check to make sure that it didn’t happen, but it is unlikely that it did.