HOUSTON -

The nation's largest retailer is rolling out new security guidelines and the new policy has some customers concerned about an exchange of information at checkout.

The three-digit security code on the back of your credit card is supposed to be top secret and consumers have been trained to guard it closely. That's why some shoppers wondered why Walmart is now asking for that code at the checkout.

"And I thought 'Oh, this isn't right,'" Denise Burris told Local 2 Consumer Expert Amy Davis. "I questioned her with it, and as soon as I walked out the door, I called Chase and I canceled my card."

Burris thought twice about punching her three-digit security code into the pay terminal at a Humble Walmart.

"The only time that I've been asked to give the three-digit security code is when I've been shopping online and I'm not in person," said Burris.

But a Walmart spokesperson confirmed it started asking for the 3-digit number almost a year ago to cut down on credit card fraud.

"Walmart has agreed with several card issuers to require the use of the three-digit security code on transactions over certain dollar thresholds," said Walmart's Dianna Gee.

"Anybody that has that card has that three-digit pin," countered Burris. "It is not a security protection."

But Walmart argues that the most common types of credit card fraud come out of data breaches.  When it happened at Target and Neiman Marcus in recent months, thieves stole the credit card information for millions of consumers. Authorities say they planned on selling the data. Other scammers could create phony cards with legitimate account numbers printed on them. Walmart says the one thing thieves don't get in those breaches is the 3-digit code on the back of your card.

"Walmart's doing the right thing on this one," said Chris Bronk, a Rice University Baker Institute Fellow in IT Policy.

Bronk says ideally the account number and the codes will be stored separately, so would-be data thieves can't get all of your information in one place.

"It really is a necessity at this point, because credit card fraud, thanks to the cyber vector, is worse than ever before."

Walmart says as soon as card issuers switch to those new chip and PIN cards, it will no longer need to ask for the three-digit security codes.