Glenn Fleishman wrote an interesting article on how to have a slightly more secure public network, but be sure and read the comments, which are at least as informative as the article.
Public WiFi is insecure. But it doesn’t have to be. If you own or manage a venue, like a coffeeshop or restaurant, and provide free and open WiFi, you can help protect your customers without having to provide technical support or waste money. The new reality is that you can offer “open” access without having an open network.