You may have noticed that when you look at products on a search engine, that same product appears as an advertisement in your social media and other sites you visit. Many search engines provide advertisers with tools for evaluating the impact of different keywords or phrases. These tools typically “track” user behavior patterns and associate products for sale by companies that subscribe to and pay for their services to help identify potential customers. On the other hand, there are also ad-blockers that block this type of communication. What constraints, if any, should be applied to this practice?