Taylor Swift secretly scanned fans through a facial-recognition system before her concert at California’s Rose Bowl this May in order to look for stalkers. The facial recognition system was built into a kiosk displaying highlights of the singer’s rehearsals. When fans looked at the kiosk, it would secretly record their faces. Afterward, the data was sent to a “command post” in Nashville, Tennessee, that worked to match hundreds of images to a database of Swift’s known stalkers. While the move might seem creepy, it’s perfectly legal. Since a concert is technically a private event, organizers can subject concert-goers to almost any kind of surveillance. Advancements in facial-recognition technology are being applied for use at crowded events, such as those at concerts. Ticketmaster is working on replacing tickets with a facial scan that is tied to your seat.