Amazon.com has a promotion for U.S. shoppers on Prime Day, the 48-hour marketing blitz that started Monday: Earn $10 of credit if you let Amazon track the websites you visit.
The deal is for new installations of the Amazon Assistant, a comparison-shopping tool that customers can add to their web browsers. It fetches Amazon's price for products that users see on Walmart.com, Target.com and elsewhere.
In order to work, the assistant needs access to users' web activity, including the links and some page content they view. The catch, as Amazon explains in the fine print, is the company can use this data to improve its general marketing, products and services, unrelated to the shopping assistant.
The terms underscore the power consumers routinely give to Amazon and other big technology companies when using their free services.