Mitch Lipka, dealnews consumer advocate When you whip out your credit card, a lot of activity is taking place behind the scenes, but the activity is different whether you are buying in a store or online. On the various credit card systems, sophisticated programs analyze purchases — or attempts at purchasing — in real-time to see whether something about the transaction seems off kilter. Those in the credit card industry say that while the various fraud defenses differ in the online and brick-and-mortar worlds, that shoppers should feel equally protected whichever way they go. But as one industry insider tells me, there's an added measure of protection for the online shopper in at least one instance: when using a debit card. Why? Because when you use your debit card in a store and punch in a PIN, that transaction doesn't necessarily go over the Visa network, which potentially negates the "Zero Liability" promise that system affords consumers. But when the purchase is made online with a debit card (and hence absent a PIN), the transaction will go over the Visa network and the fraud guarantee will be in place. American Express spokeswoman Marina Hoffmann Norville says fraud protection in place for both online and in-person shoppers is designed to try to "guarantee the authenticity of the transaction." "Every single American Express charge, whether it's online or offline goes through a fraud screen," she says. "There are different fraud controls in place for both." While it might seem more likely that the invisibility of the online purchaser would lend itself more to fraud, Norville points out that it is no more a risk than if a crook had stolen someone's card and tried to use it at a store. American Express, MasterCard and Visa do not disclose what specific screening is in place — citing the obvious reason of not wanting to tip off criminals to how to beat the system. All tout their fraud protection and pledge to remove any phony charge. Here are a few things to keep in mind to have some peace of mind when shopping online: Look for "https" to precede the web address when you're making a transaction so you know your information is being encrypted Review the charges on your card and file a dispute against any that you did not make. Although a debit card can have the layer of protection described above, it is safer to use a credit card and not place your cash at risk. When buying with a credit card, which makes you feel safer?customer surveys Mitch Lipka is an investigative journalist for consumer issues who formerly wrote for WalletPop.com, Consumer Reports, the Philadelphia Inquirer and the Fort Lauderdale Sun-Sentinel, among other places. Follow him on Twitter — @mitchlipka or on Facebook. You can also sign up for an email alert for all dealnews features.