MAC Address - Media Access Control Address. An identification code assigned to network connected devices. It uniquely identifies every device on a network.
MAC addresses comprise six groups of two hexadecimal digits. In mobile phones, they can be used to identify people.
The addresses are "pseudonymised". This means that additional information is needed to connect the data to a person. However, pseudonymised data can still be used to single individuals out and combine their data from different records.
Mobile device manufacturers increasingly deploy MAC address randomisation to try to protect user privacy and the persistent hardware identifiers being tracked. There are many phones in wide use that do not effectively prevent tracking
Devices continually send out Probe Requests to scan for available access points. This has the side effect of announcing their presence and trackable identity information to every nearby eavesdropper.
Media Access Control (MAC) address randomization involves sending a random identifier in network transmissions in place of the fixed identifier, in an attempt to improve privacy.
Further ReadingWhy you shouldn’t use mobile phone signals to count people: Dutch city fined €600000
Three Years Later: A Study of MAC Address Randomization In Mobile Devices And When It Succeeds. July 2021Proceedings on Privacy Enhancing Technologies 2021(3):164-181