Taylor Swift and Elon Musk have something in common: They don't want real-time location data for their private jets published online for all to see.

But in the United States, aircraft data is legally available for real-time tracking, something experts say is critical for safety and efficiency. Websites that track commercial flights use and publish it to provide consumer insights like on-time records, but the same data can be scooped up by virtually anyone looking to follow private planes with celebrities and other public figures, too.

Musk famously banned accounts on X, formerly Twitter, that shared the whereabouts of his jet and in recent months, Swift's lawyers demanded that accounts on the platform stop tracking her plane. They fired off letters to a college student behind an assortment of tracking accounts, Jack Sweeney, according to the Washington Post, alleging the only public need for the information was "to stalk, harass, and exert dominion and control.”

The problem for celebrities worried about obsessive fans and ill-wishers following their every move is that what Sweeney is doing isn't really illegal, because the information he shares is based on publicly available data. Still, experts and advocates say there is valid concern for private jet owners.

Dan Hubbard, a spokesperson for the National Business Aviation Association, said technology developed in recent years has expanded the availability of the information and increased danger to people using private planes by allowing them to be "tracked in real time by anyone, anywhere in the world with an internet connection, and any motive."

How is Taylor Swift's jet being tracked?

Sweeney has several social media accounts tracking lots of different aircraft belonging to celebrities, billionaires, Russian oligarchs and politicians. Some of the accounts also analyze the carbon footprint of the jet owners' trips.

The information doesn't come from a single source. It includes data pieced together from a few different sources of publicly available information, including registration information from the Federal Aviation Administration, and broadcast signals from the planes themselves. Those signals are known as Automatic Dependent Surveillance-Broadcast, or ADS-B, data.

ADS-B technology is required by the Federal Aviation Administration on aircraft and shares real-time position, altitude and other information that is important to flight traffic controllers. The data also allows for sites like FlightAware.com to show real-time commercial flight locations.

The technology is "groundbreaking" for safety and the efficiency of flight routes, Hubbard said. The FAA and Congress for years have made sure there are ways for jet owners with safety and privacy concerns to opt-out of real-time data sharing, Hubbard said. But that doesn't stop the planes from transmitting it.

How is real-time location tracking legal?

The equipment needed to receive ADS-B transmissions is available cheaply to practically anyone, and websites publishing flight data that they get from the planes themselves don't have to follow FAA's opt-out rules.

Sites like ADS-B Exchange crowd source data from aviation hobbyists all over the country who have the right equipment, giving a pretty accurate real-time picture of where planes are – including private ones whose owners ask the FAA to suppress that information. The data can tell you where the plane takes off and lands, but not necessarily who is on it.

The founder of ADS-B Exchange told NBC News in 2022 it wasn't made for people to stalk celebrities. "The purpose of this is not for being a paparazzi. It’s for aviation enthusiasts," Dan Streufert said, adding that the site doesn't take down public figures' data because it isn't an arbiter of information that's already widely available.

What about privacy concerns?

Musk and Swift have both cited threats to their safety. Swift's attorneys said in a letter provided to the Post that Sweeney's accounts have done “direct and irreparable harm, as well as emotional and physical distress,” and caused Swift to fear for her personal safety.

Sweeney has previously said that he recognizes safety concerns, but that his social media accounts are simply sharing information that's already public.

"I think there is a valid concern, but now (Musk is) trying to say it's private data," Sweeney told USA TODAY in 2022 after Musk permanently banned his account @ElonJet from X/Twitter. "And it’s all out there. It’s not like I’m hacking a system or anything. It’s all out there. "

"And if it's a safety concern, then something further up... needs to be fixed," he wrote, such as with regulatory agencies like the FAA.

Hubbard, of the National Business Aviation Association, said safety is a legitimate concern, citing an incident that posed a security threat to veterans returning to their home airports, only to be met by anti-war protesters who followed flight information.

"Often, the development of technology can have unintended outcomes," Hubbard said. "What you’re seeing, then, is this kind of tracking, this kind of flight stalking, which really is problematic on several levels."

Is publishing a flight's location considered stalking?

Though Swift's lawyers said Sweeney's actions were "stalking and harassing behavior," privacy and technology experts say that under the law, tracking the flights and publishing their locations doesn't constitute stalking or "doxxing" – revealing personal information such as addresses to target someone for harm or abuse.

Chris Hoofnagle, a professor of law at University of California, Berkeley, who focuses on the interplay of law and technology, said “merely posting publicly-available information does not meet state law definitions of stalking."

Jasmine McNealy, an associate professor at the University of Florida whose research focuses on digital privacy, said while there may be valid safety concerns from celebrity private-jet users, Sweeney’s posts and the operation of flight tracking websites don't have the malicious intent required to be considered stalking or doxxing.

“What the student has done here is make [public information] more visible,” McNealy told USA TODAY, adding that the rapid development of technology has made it easier to collect and share information that may have always been publicly available but harder to find, drawing the ire of some public figures.