Stuart A. Thompson and Charlie Warzel write:

If you own a mobile phone, its every move is logged and tracked by dozens of companies. No one is beyond the reach of this constant digital surveillance. Not even the president of the United States.

The Times Privacy Project obtained a dataset with more than 50 billion location pings from the phones of more than 12 million people in this country. It was a random sample from 2016 and 2017, but it took only minutes — with assistance from publicly available information — for us to deanonymize location data and track the whereabouts of President Trump.

A single dot appeared on the screen, representing the precise location of someone in President Trump’s entourage at 7:10 a.m. It lingered around the grounds of the president’s Mar-a-Lago Club in Palm Beach, Fla., where the president was staying, for about an hour.

Then it was on the move.

The dot traveled to the Trump National Golf Club in Jupiter, about 30 minutes north of the hotel, pinging again at 9:24 a.m. just outside the compound. The president was there to play golf with Prime Minister Shinzo Abe of Japan.

There the dot stayed until at least 1:12 p.m., when it moved to the Trump International Golf Club in West Palm Beach, where the world leaders enjoyed a private lunch.

By 5:08 p.m., the phone was back at Mar-a-Lago.

The president had what he called a working dinner with Mr. Abe that night.

The device’s owner was easy to trace, revealing the outline of the person’s work and life. The same phone pinged a dozen times at the nearby Secret Service field office and events with elected officials. From computer screens more than 1,000 miles away, we could watch the person travel from exclusive areas at Palm Beach International Airport to Mar-a-Lago.

The meticulous movements — down to a few feet — of the president’s entourage were recorded by a smartphone we believe belonged to a Secret Service agent, whose home was also clearly identifiable in the data. Connecting the home to public deeds revealed the person’s name, along with the name of the person’s spouse, exposing even more details about both families. We could also see other stops this person made, apparently more connected with his private life than his public duties. The Secret Service declined to comment on our findings or describe its policies regarding location data.

The vulnerability of the person we tracked in Mr. Trump’s entourage is one that many if not all of us share: the apps (weather services, maps, perhaps even something as mundane as a coupon saver) collecting and sharing his location on his phone.

Americans have grown eerily accustomed to being tracked throughout their digital lives. But it’s far from their fault. It’s a result of a system in which data surveillance practices are hidden from consumers and in which much of the collection of information is done without the full knowledge of the device holders.

For the nation’s security agencies, however, privacy is critical to the safety of military, defense and security operations across the country and abroad. If threats to that privacy have seemed abstract in the past, the trove of location data we have analyzed has brought them into sharp relief. Military and intelligence officials have long been concerned about how their movements could be exposed; now every move is. As a senior Defense Department official told Times Opinion, even the Pentagon has told employees to expect that their privacy is compromised:

“We want our people to understand: They should make no assumptions about anonymity. You are not anonymous on this planet at this point in our existence. Everyone is trackable, traceable, discoverable to some degree.”

We were able to track smartphones in nearly every major government building and facility in Washington. We could follow them back to homes and, ultimately, their owners’ true identities. Even a prominent senator’s national security adviser — someone for whom privacy and security are core to their every working day — was identified and tracked in the data. [Continue reading…]