Tracking madness, New York Times investigation.

"People consent to be tracked, the data is anonymous and the data is secure."
sure...

Every minute of every day, everywhere on the planet, dozens of companies — largely unregulated, little scrutinized — are logging the movements of tens of millions of people with mobile phones and storing the information in gigantic data files

You’ve probably never heard of most of the companies — and yet to anyone who has access to this data, your life is an open book. They can see the places you go every moment of the day,

...the location data contains billions of data points with no identifiable information like names or email addresses. But it’s child’s play to connect real names to the dots that appear on the maps.

...the Women’s March, as a crowd of nearly half a million descended on the capital. Examining just a photo from the event, you might be hard-pressed to tie a face to a name. But in our data, pings at the protest connected to clear trails through the data, documenting the lives of protesters in the months before and after the protest, including where they lived and worked. We spotted a senior official at the Department of Defense walking through the Women’s March, beginning on the National Mall and moving past the Smithsonian National Museum of American History that afternoon. His wife was also on the mall that day, something we discovered after tracking him to his home in Virginia.

https://www.nytimes.com/interactive/2019/12/19/opinion/location-tracking-cell-phone.html