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.

Source: Google and Mastercard Cut a Secret Ad Deal to Track Retail Sales – Bloomberg

Google insists that while they may be smoking Mastercard data, they insist they do not inhale. Yet they have access to 70 percent of all credit and debit card purchases.