There was one wireless ISP many years ago in a city I lived in that had a signal/reception page to see your signal to their closet tower. The URL included the c

There was one wireless ISP many years ago in a city I lived in that had a signal/reception page to see your signal to their closet tower. The URL included the customer number to identify your location. I quickly discovered it had no authorisation checks. You could easily find the exact addresses of all of their customers. Inactive/old customers returned no data.