The car would have to be somewhere that the potential thief would see often. No use in walking up to a car in a parking lot, getting the VIN and going to get a key made. The car won't be there. But if the car is in someones driveway then they can just walk up, grab the VIN and be on their way. I'm not sure about how posting it online would be different... would someone in Cali get a key made then drive out the IL to find the potential car? IMHO, it's more dangerous parking outside than it is that a person will make a key and steal your car... no harm no foul.