When Elon Musk offered Jack Sweeney $5,000 to shut down a Twitter account tracking his flight patterns, a lightbulb lit up in Sweeney’s head: This coding project, set up mostly for kicks, could become extremely profitable.

Sweeney, 19, is a freshman studying information technology at the University of Central Florida. In June 2020, the self-professed Musk fan wrote some code to source the billionaire’s flight information from public websites like ADS-B Exchange, which monitor data like location, altitude and speed transmitted by every federally regulated aircraft.

He set the data to auto-publish to a Twitter account, @ElonJet — and in mere months, hundreds of thousands of people started following it. Buoyed by popular demand, Sweeney wrote new code to follow other notable private planes, a bulk of them added in summer 2021, he tells CNBC Make It.

Sweeney now tracks flight data from 127 different jets, including aircrafts owned by Bill Gates, Jeff Bezos and former president Donald Trump. That data appears on 16 different Twitter accounts, with @ElonJet still the most popular at more than 300,000 followers.