Rolling Stone: “Spying on presidents used to be a tough business. One of the great unsung heroes of American history was a formerly enslaved woman named Mary Bowser, a spy who infiltrated the family of Jefferson Davis as a domestic servant, and eventually landed a full-time job in the Southern White House, the political seat of his Confederacy. Armed with a photographic memory and an all-access pass to the inner workings of the Davis administration, she fed details daily to the Union army, which Ulysses S. Grant called the “most valuable information” he received from the Southern capital during the war. These days, it’s a whole lot easier. While researching our new book, The Secret Life of Data, we gathered some sensitive information from Mar-a-Lago, Donald Trump’s Palm Beach club, which he used as a base for political operations both during and after his presidency. He even referred to on several occasions as his “Southern White House.”

We didn’t have to risk life and limb, posing as the help and smuggling information out through a well-funded spy ring. All we had to do was sign up for an online service, enter the address of Mar-a-Lago, and click a button. Within a few minutes, we had a report profiling thousands of visitors to Trump’s club over the course of an entire year, including details like where they likely live and work, their ages, incomes, ethnicities, education levels, where they were immediately before visiting, and where they spent their time on the property once they got there. This wasn’t some dark web hacker thing. No Bitcoin was exchanged. The service we used was perfectly legal and freely available on the open web, one of dozens of “data brokers” that collect and trade in consumer data. It’s a $300-billion-per-year business — about the same as the gross domestic product of Hong Kong. This particular data broker, called Near, uses smartphone location data to trace the foot traffic of about 1.6 billion people across 70 million locations in 44 countries…”