When my son was younger - maybe 9 or 10 or so, we were on a plane and he was using his phone and I looked over his shoulder and realized he was on the internet... but I hadn't paid for an internet plan. I said, "son, how are you using the internet?" He said, "oh, a kid at school showed me - if you go here" (he opened up the wifi settings where the DHCP assigned IP address is) "and start changing the numbers, eventually the internet will work." Apparently, at the time, on American Airlines, when somebody bought and paid for an internet plan, it gave them an IP address and authorized it to use the internet... if somebody else guessed your IP address (which was pretty easy, it was a 192.168 address) and spoofed it, they could take over your internet connection with no further authorization.

I had to tell him not to do that, but I was kind of proud of him for having the temerity to go for it.