»More on hax0ring the MTA

from disinformation:

Apparently the exploit is a result of the system being unable to read bent or damaged cards. To compensate for that error there is a built in fail safe that if a card is swiped 3 times and the computer reads a certain code that tells them it was damaged, on the 4th swipe it lets the swiper through. I guess they figure if someone is using a empty card they they wouldn't swipe it 4 times. Guess again!

Here's how it works:

1) Bend the bottom right corner of your metro card up to the f (f part of the word facing). It is a 45 degree angle. Close the bend hard
2) Swipe it 3 times and it says "please swipe again"
3) On the 3rd time it says "please swipe again at this turnstile"
4) Swipe one more time with the bend open and it says balance= $0.00, previous balance $2.00. GO
5) Go.

How many MetroCard exploits are there?