Analyses have become so sophisticated that even after stripping away almost all personal information, it is possible to track a person from their transactions – even when those transactions are mixed in with a million other people.
The bank stripped away names, credit card numbers, shop addresses, and even the exact times of the transactions. All that remained were the metadata: amounts spent, shop type—restaurant, gym, or grocery store, for example—and a code representing each person. – “Credit Card Study Blows Holes In Anonymity“, Science Magazine
Take the credit card transaction data, cross-reference to social media or security footage, and much of a person’s privacy evaporates.