My mastercard had the same feature sometime along the way that they advertised strongly to me on the website. I think I might have used it once, but it was too much of a hassle to log in to my account, generate the number, go back to the website that I was purchasing from, etc.

Hell, i just looked it up and they still have it: https://www.cardbenefits.citi.com/Products/Virtual-Account-N...