    Sentence 1: Is there an app that notifies  website visitor through a widget that  someone recently purchased a product?    Sentence 2: Recently I had purchased a  product from an online shopping website  (Amazon). After that. incident, I am  followed. by an annoying advertisement of  various shopping sites on that product in  each and every website I visit. How did all  the websites I'visits know about my interest  in thatproduct?