[3] If a payment card contains an MM code as well as a magnetic stripe, any fraudster who counterfeits the card but fails to read and duplicate the MM code onto the copy will be detected when trying to use the counterfeit in a German automated teller machine.
The MM code consists of two components, one stored on the magnetic stripe, and one hidden inside the card's material.
Since the arrival of the EMV chip-based payment protocols, the MM code has reduced significance in combatting card counterfeiting.
The MM feature is encoded in the middle layer of an ISO/IEC 7810 card as a bar code formed by two materials with different electrical properties.
It reads a second data stripe that, unlike the magstripe, cannot easily be rewritten with off-the-shelf equipment.