Quoting an article by Louise Matsakis in the Wired web site:

“On the internet, the personal data users give away for free is transformed into a precious commodity. The puppy photos people upload train machines to be smarter. The questions they ask Google uncover humanity’s deepest prejudices. And their location histories tell investors which stores attract the most shoppers. Even seemingly benign activities, like staying in and watching a movie, generate mountains of information, treasure to be scooped up later by businesses of all kinds.

“Personal data is often compared to oil—it powers today’s most profitable corporations, just like fossil fuels energized those of the past. But the consumers it’s extracted from often know little about how much of their information is collected, who gets to look at it, and what it’s worth. Every day, hundreds of companies you may not even know exist gather facts about you, some more intimate than others. That information may then flow to academic researchers, hackers, law enforcement, and foreign nations—as well as plenty of companies trying to sell you stuff.”

This interesting article is highly recommended reading for all computer users. You might want to read it at: https://www.wired.com/story/wired-guide-personal-data-collection/.