Tiffany Hsu reports:
The punch cards stuffed in your wallet know next to nothing about you, except maybe how many frozen yogurts you still need to buy to get a free one.
But loyalty programs, as they shift from paper and plastic to apps and websites, are increasingly tracking a currency that can be more valuable than how much you spend: personal data. As a result, the programs know things about you that some of your friends may not, like your favorite flavor (mango), when your cravings strike (early afternoon) and how you pay (with your Visa), in addition to billing details and contact information.
Hackers are in close pursuit.
Read more on The New York Times.