In my university all vending machines use a Mifare Classic NFC tag to save users' credit. It has almost become a tradition that each year at the beginning of th

In my university all vending machines use a Mifare Classic NFC tag to save users' credit. It has almost become a tradition that each year at the beginning of the second semester some freshmen find out how to read and modify their credit and mess up the vending machine system for some days just for the lulz and for (a very modest) profit.