Is your "Free Wi-Fi" really free?

Many cafès, hotels and shopping centres are offering what they call "free wi-fi", but when users will connect to that network, the company will tap into all network requests and replace them with an HTML page, prompting user to "register or log-in" in order be allowed to have access to the internet.

So, in practice, it is not not a free wi-fi, neither ethically, nor in terms of price: because users pay companies by giving away their personal data. That could then be used by company to sell advertisements, snoop on people or resell this personal data.

These are some of nasty non-free networks that I have come across: