Amazon is sending shoppers free samples of products — curated to their tastes — as part of the company's push into advertising.

The program seems like a sweet deal: Products you'll like, free of charge, waiting on your doorstep. But below the surface it raises some privacy concerns in the age of data mining and detailed digital user profiles.

"Amazon surprises select customers with samples that we think will be delightful and helpful," the company says on its website. "It's like Amazon's product recommendations, but real, so you can try, smell, feel and taste the latest products. There is no obligation to purchase or review the product and you can opt out at any time."

The company will send samples based on a shopper's purchasing history, according to Axios, which first spotted the program. Amazon markets the feature to brands using its wide swath of user data to "put their products in the hands of the right customers," Axios reports.

Amazon did not immediately return request for comment.

Amazon has been stealthily taking market share of the advertising industry from long-time leaders Facebook and Google. And the company has an advantage in this type of campaign with purchase histories and preferred shipping addresses.

But Amazon will toe a precarious line in marketing to brands based on user information. That's what got Facebook into hot water this past year and drew intense scrutiny to ad-based business models more broadly.

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