I've noticed that a number of brick-and-mortar stores have begun asking me for the last four digits of my credit card when using that mechanism to pay for my purchase. When asked about this, I've been informed that some people have been replacing the magnetic stripe on the card with a different one, so that the numbers on the magstripe are different from the numbers imprinted on the card.
In most instances so far, I have been asked to verbally recite the numbers, or to type them into a keypad. I fail to see how this prevents the sort of card counterfeiting it is intended to stop. If I really wanted to execute this kind of crime, I would merely have to purchase a tank of gas with the phony card first: almost all gas stations print the last four digits of the card on the receipt!
The only meaningful way to prevent this kind of fraud is if one were asked to surrender the card, so that the clerk could verify the digits themselves.