Wireless user device probe data can be used to infer or determine an attribute of a user. The probe data can be captured by a sensor device from probes wirelessly transmitted by the user device to search for wireless access points. The probe data can include network addresses of the wireless access points to which the user device has wirelessly connected. The probe data can also include connection information about wireless links between the user device and the wireless access points. The probe data and a user device identifier can be transmitted to a computing device that can compare the probe data to access point network addresses associated with attributes in an electronic data store to determine an attribute for a user of the user device.