Citing "four people with the knowledge of the deal, three of whom worked on it directly", the magazine that the agreement, which is bound to stoke new privacy concerns, was the fruit of four years of negotiations. If you spend money on Google or Facebook ads, you can directly track the number of customers who end up on your online store because of your campaign.
Google and Mastercard have had a secret partnership for the past year in which the credit card company has shared US transaction data with the tech giant, according to a report by Bloomberg. If, within 30 days, they then use a Mastercard to buy that item in a physical store, Google will notify the advertiser as part of its reporting on ad effectiveness. The spokesperson noted that users can opt out of the ad tracking tool by opting out of "Web and App Activity" online console.
Google also has deals with several third-party companies that process card transaction data.
"People don't expect what they buy physically in a store to be linked to what they are buying online", said Christine Bannon, counsel with the advocacy group Electronic Privacy Information Centre (EPIC).
It turns out Google is doing it, too. The search giant actually announced this program under the name "Store Sales Measurement" a year ago, claiming that it was able to record 70% of U.S. credit and debit card transactions via third-party partnerships.
One of the most recent examples of Google going to arguably questionable lengths to acquire data is its deal with MasterCard.
According to anonymous tipsters speaking with Bloomberg, Google has had discussions with other credit card companies about partnerships, and ad agencies have approached Google about tracking even more offline information about customers, such as the time of the transactions and how much was spent.
Last year, when Google first announced the Store Sales Measurement service, the company claimed to have access to "approximately 70 percent" of United States credit and debit cards.
The company constantly tracks what you click on if you have a Google account - which includes anyone with a YouTube or Gmail account.
"No individual transaction or personal data is provided", he said in a statement. The firms help advertisers and merchants predict consumer spending behavior using cardholder data.
Mastercard says it can only see a retailer's name and the transaction amount, not the products purchased, when a consumer buys something online or offline.