Students at the University of Waterloo in Canada discovered that 'intelligent' vending machines on campus were using facial recognition without their knowledge.

The facial recognition capability was accidentally found by a student after an error message appeared on a screen of one of the M&M-branded vending machines. Students then began to cover a tiny hole apparently concealing the camera with chewing gum and sticky notes. 

They also discovered online a a brochure for the machines which revealed that they were installed with a 'demographic sensor' allowing them to calculate the age and gender of anyone that approaches and make 'AI-powered product recommendations.'

Invenda said the vending machines do not store or transmit personally identifiable imagery.

However, the university demanded the software was disabled and machines removed from campus.