They can also be tracked by their history if you have othe data sources. Let’s say you have cell phone data of someone. You can then correlate that with place (

They can also be tracked by their history if you have othe data sources. Let’s say you have cell phone data of someone. You can then correlate that with place (let’s say home and work) and time of a few purchases. This then de-anonymizes the card and the other purchases, even if they had their cellphone turned of in the delicate purchases.