In an extensive report that is part of its “Privacy Project,” The New York Times revealed Thursday that it has gained access to cell phone tracking data for millions of Americans and was able to rather easily track the movements of regular Americans as well as high-profile and powerful figures, including President Trump himself — details of whose actions the Times published in a follow-up report.

In its initial report, titled “Twelve Million Phones, One Dataset, Zero Privacy,” the Times warns that if you were able to see the data which they obtained from a single private cell phone app company, “you might never use your phone the same way again.”

“The data was provided to Times Opinion by sources who asked to remain anonymous because they were not authorized to share it and could face severe penalties for doing so,” the Times explains. “The sources of the information said they had grown alarmed about how it might be abused and urgently wanted to inform the public and lawmakers.”

The single data file the Times obtained is “by far the largest and most sensitive ever to be reviewed by journalists,” the Times claims, containing “more than 50 billion location pings from the phones of more than 12 million Americans as they moved through several major cities, including Washington, New York, San Francisco and Los Angeles.” That data covers a period of several months in 2016 and 2017, the Times notes.

Times researchers spent “months” analyzing the data, and in that time tracked cell phone activity involving some very famous names. “One search turned up more than a dozen people visiting the Playboy Mansion, some overnight,” the Times reports. “Without much effort we spotted visitors to the estates of Johnny Depp, Tiger Woods and Arnold Schwarzenegger, connecting the devices’ owners to the residences indefinitely.” They also took some time to track the movements of participants at both pro-Trump and anti-Trump rallies.

Using the data — which the Times notes can be legally obtained by companies, who defend collecting the data because it is “anonymous” and app users give their “consent” to being tracked — the Times says they spent most of their attention “identifying people in positions of power”:

With the help of publicly available information, like home addresses, we easily identified and then tracked scores of notables. We followed military officials with security clearances as they drove home at night. We tracked law enforcement officers as they took their kids to school. We watched high-powered lawyers (and their guests) as they traveled from private jets to vacation properties. We did not name any of the people we identified without their permission. The data set is large enough that it surely points to scandal and crime but our purpose wasn’t to dig up dirt. We wanted to document the risk of underregulated surveillance. Watching dots move across a map sometimes revealed hints of faltering marriages, evidence of drug addiction, records of visits to psychological facilities.

In a follow-up report titled “How to Track President Trump,” the Times reveals that it easily followed the movements of Trump — even providing a map of those movements — by simply identifying a cell phone owned by a person in his entourage:

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.

Read the initial report here.