Most credit cards are 3D secure as a free service offered to users. It is the merchants who opt in to providing this level of protection to buyers on their site. If they do, there should be a logo on the site identifying them as using 3D secure. When making a purchase using a 3D secure card on a site that has opted in, a cardholder may be asked to provide additional information to verify that they are who they say they are to maintain the security of the transaction.