Google is using billions of credit card transaction records to determine if its online ads are working, even if customers are purchasing items in brick-and-mortar stores, the company announced Tuesday. Industry insiders described this as the "holy grail" of online advertising, according to The Washington Post.

While the advance in technology allows Google to understand purchase activity and establishes the number of sales created by digital ad campaigns, it also renews privacy debates as to how the company is using customers' personal information. Google already analyzes user data through their apps like Gmail, Google Maps and YouTube. But the new system will allow Google to connect that information with purchases made outside of the digital world.

Google currently captures 70 percent of all credit and debit card transactions through unnamed partner firms, The Washington Post reports. However, Google declined to comment on how the new system operates or what companies are sifting through these transaction records on Google's behalf, according to The Washington Post.

"While we developed the concept for this product years ago, it required years of effort to develop a solution that could meet our stringent user privacy requirements," Google said in a statement. "To accomplish this, we developed a new, custom encryption technology that ensures users' data remains private, secure, and anonymous."