The time you browsed, the items you researched, the sites you visited, Google has captured. And that information has value. That data helps advertisers and their clever algorithms customize ads that match your interests and insert them on the web pages you visit. Even your mouse movements are useful — they tell Google which ads you hovered over but didn’t click on. Sharp hedge fund managers will also buy that information, not to spam you with ads, but to help them analyze trends and find the next company to invest in. Those selfies you post to Instagram might be used by some developers to train their facial recognition software. It might be benign for your phone to use its camera to recognize your face, but that same technology helps the Chinese government maintain Big Brother-like control of its population.