I repair ATM's (among other bank equipment) for a living and can say that that is FALSE. If you enter your PIN backwards the next screen you see will simply tell you that it was entered incorrectly and to please try again. I think that the origins of this come from ATM's that have an ambush alarm on the vault portion of the machine. The ambush alarm trips when an operator who is forced to open the vault dials the last number of the combination either 10 numbers higher or lower than the actual number. The higher or lower part is predetemined by the bank, the network, and the alarm provider. Not all ATM's have ambush set up on them however.