A magstripe card, or magnetic stripe card store static information in the stripe on the back of the card. That means the same information transmits to the bank each time the person swipes the card. Once a person has that information, it’s available for them to use it repeatedly.
The magstripe is made up of tiny iron-based magnetic particles in a plastic-like film. Each particle is really a very tiny bar magnet about 20 millionths of an inch long.