angry tapir writes: The probe requests emitted by a smartphone as it seeks a Wi-Fi network to connect reveal the device's manufacturer thanks to its MAC address. This can offer some information about a crowd of people by looking at the breakdown by device brand. However, because some OSes include a preferred network list (PNL) in their probes, it may be possible to use Wi-Fi sniffing to infer even more information about a group of people by looking for common SSIDs, and potentially mapping them to known network locations. A group of Italian researchers has been looking at ways to use the information in probe requests to analyse the social connections of crowds.
Never ask two questions in a business letter. The reply will discuss
the one you are least interested, and say nothing about the other.