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A virtual card is basically just a number specifically generated for you to pay for your purchases online. This number is connected with your account and allows you to draw money in a secure way without endangering your real account. There is no difference for the online merchant between a virtual card or a physical card, but in this way a merchant doesn't have an access to an original account, hence no opportunity to steal.
Virtual cards can be created for debit and credit cards, there also can be virtual prepaid cards, not connected to any account at all. Those are just loaded or reloaded with money and used for online purchases. Note that you can’t use a virtual card as an original card in offline shops, they are non-physical. Virtual cards usually expire quite soon, they can exist for just one transaction for safety purposes or function for about a year. Their main advantage is that virtual cards numbers are impossible to track back to the original number, besides it’s impossible to clone such cards, all of this making the transactions safer.
There are special services for creating a one time card that expires as soon as you make a purchase. These are not connected to any bank, they act like an intermediary between you and the vendor. As a result the vendor can't get to your money. You can set a charge limit, so a fraudster can't max out your card and no fraudulent charges can be made to your account. One of the ways is to set the limit exactly to the sum you are planning to pay, so if you are purchasing a camera for $300, set the limit to $300 and there will be literally nothing else to charge.
Creating a virtual number on such a service requires a minute fee usually not bigger than $5, but that seems more than a fair price for safe sleep. In fact, with as many as 46% Americans affected by credit card fraud in the past 5 years, getting a virtual one should be a must for all vigilant citizens out there.
Whether such card is available to you depends on your credit card issuer. Some banks offer such a service, some don't. Mostly MasterCard deals with virtual prepaid cards, but really this is an option you should check with a card issuer. As a first step towards a MasterCard virtual card you can find a collection of MasterCard credit cards that you can apply for if you find a suitable one for you.