I plugged my iPhone 7 into my Windows 10 PC at home and was surprised to see that my phone, which usually has mobile hotspot turned *off*, showed 1 hotspot connection. After a little digging, I found that by plugging it into my PC, hotspot had been automatically enabled, and the PC was using it as a tether. What's more, my PC was preferring it over its *regular* internet connection, and I'd accidentally downloaded a couple albums to my PC using mobile hotspot and used up 700MB of cellular data in a few minutes. This didn't used to happen, so I suspect something changed on the PC side, either an iTunes updates or something with a recent Windows update (maybe the Spring feature update). The solution was to go to my network connections in control panel and disable the iPhone connection. Disabling it seemed to persist across disconnecting/reconnecting the phone. So if you're like me, still old-fashioned, and preferring to sync/backup your iPhone over iTunes, keep an eye out for this so you don't accidentally use up all your data with an unintentional mobile tether.