Students at the University of Waterloo in Ontario, Canada were shocked when they discovered that a vending machine on the campus was using facial recognition software without their consent, CBN reports.

Students only became aware that the M&M vending machine was doing this when a fourth-year computer student, River Stanley, reported an unusual error that popped up on its display while he was making a purchase. It read: “Invenda.Vending. FacialRecognition.App.exe — Application error.”

When Stanley wrote about his discovery in one of the university’s newsletters, MathNews, he asked, “Why does it have a facial recognition app? How can this error even exist? We wouldn’t have known if it weren’t for the application error. There’s no warning here.”

The students were predictably outraged and responded by putting tape and post-it notes over the machine’s sensors.

The manufacturer of the machines, Invenda, a Swiss-based company, stated that the software does not collect or store images, but rather uses it to determine when someone is about to make a purchase, so it can activate its software.

“However, according to the Invenda website, the Smart Vending Machines can detect the presence of a person, their estimated age, and gender,” Talia Wise noted in her article for CBN.

Because of the outrage, university officials have since announced that all the 29 vending machines that were doing this would be removed.