yep, or worse, like shut off the power grid. My local electric co-op has an open wifi port a white hat hacker friend of mine uses for free. he said in very short order he could have the town in a blackout if he wanted to. my town is about 20,000 people. No big deal. But try that in a city such as toronto canada, who recently went wifi on their power companies. An open wifi port could cause a lot more damage.
I have found open ports on unprotected Wi-Fi at a major bank in North Carolina and at a major power company, both across the street from each other. Need I say more? Scary stuff -- and the IT departments weren't even aware that some bean counter decided to bring his own Wi-Fi equipment and connect to their network. The RF signal shot straight out the skyscraper windows to all the other buildings in the neighborhood.