Bloomberg reporting, circa 2018:
“For the past year, select Google advertisers have had access to a potent new tool to track whether the ads they ran online led to a sale at a physical store in the U.S. That insight came thanks in part to a stockpile of Mastercard transactions that Google paid for...”
“But most of the two billion Mastercard holders aren’t aware of this behind-the-scenes tracking. That’s because the companies never told the public about the arrangement. .... But the deal, which has not been previously reported, could raise broader privacy concerns about how much consumer data technology companies like Google quietly absorb.”
https://www.bloomberg.com/news/articles/2018-08-30/google-an...