What are Wi-Fi probe requests?
Probe requests are sent by a station to elicit information about access points, in particular to determine if an access point is present or not in the nearby environment. Some devices (mostly smartphones and tablets) use these requests to determine if one of the networks they have previously been connected to is in range, leaking their preferred network list (PNL) and, therefore, your personal information.
Below is a typical Wi-Fi authentication process between a mobile station (for example, your smartphone) and an access point (AP):
Step 1 is optional (and therefore, step 2) since the access points announce their presence by broadcasting their name (ESSID) using beacon frames. Consequently, it is not necessary to rely on probe requests to get the list of the access points available. It is a design choice that, although it speeds up the discovery process, causes privacy and security issues.
ProbeQuest can be used to leverage this leak of information to conduct diverse social engineering and network attacks.