Forget Milk and Eggs: Supermarkets Are Having a Fire Sale on Data About You

When you use supermarket discount cards, you are sharing much more than what is in your cart. From a report: When you hit the checkout line at your local supermarket and give the cashier your phone number or loyalty card, you are handing over a valuable treasure trove of data that may not be limited to the items in your shopping cart. Many grocers systematically infer information about you from your purchases and "enrich" the personal information you provide with additional data from third-party