Wi-Fi Sniffing Lets Researchers Build Graph of Offline Social Networks

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 (PDF). A group of Italian researchers has been looking at ways to use the information in probe requests to analyze the social connections of crowds." The idea being that if you share preferred networks (especially ones only seen infrequently) you are more likely to be socially connected.

Illegal

[Solandri]

Didn't you get the memo? The courts think sniffing open wifi networks is a violation of wiretap laws [slashdot.org].

Re:Another example of data "leakage"

[jrumney]

Because some people configure their access points to not broadcast the SSID in the misguided belief that they can add a layer of security by doing that, devices will actively try to connect to networks that they cannot see. So anyone anywhere can see your device periodically trying to connect to every network that it is configured to connect to automatically. This doesn't save battery life, if anything it uses more than sitting passively listening for known networks would, but the idiocy of hidden SSIDs is widespread enough that it is necessary for WiFi to just work for mobile devices.