Arcade debit card security

How secure are the debit cards we use at arcade centres? (I mean the ones you put money into and swipe into game machines)

Is the data even encrypted?

If not, can someone purchase a device that can modify the data on such cards, to increase the money on them?

If yes, does the same key get used everytime?

Notes:

1. 
   

   The card used is an ordinary card with a single magnetic strip. All cards look exactly the same. They might be having unique numbers, though (which are not printed anywhere).

   
   


2. 
   

   The machines do not appear to be connected to any server (but I can't say for sure). They have only a single cable that connects directly to the power supply. There is no visible wireless network (which they could be using) in that zone.

   
   


3. 
   

   The machines have an outlet where the card can be swiped. It has a tiny screen (2 lines of text only) that shows the price per game. It shows you only your remaining balance when you swipe the card and starts the game. The swiping part doesn't seem to interact with the game except for starting it.

   
   


4. 
   

   @AndreDaniel mentioned that reverse engineering would take a lot of effort. Maybe one could buy a card with real money and copy the entire code as it is, to his computer. After using the card (and spending all the money), he could format the data, and copy the original data from his computer to the card.