Google and Mastercard cut a secret ad deal to track retail sales

Labels of digital payment (from top) WeChat Pay, Alipay, American Express, Electronic Payment Services (EPS), MasterCard, VISA and UnionPay are displayed outside a store selling watches at a shopping mall in Hong Kong, China July 31, 2018. Picture taken July 31, 2018. REUTERS/Bobby Yip

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 US. 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.