I think PayPal used to do it through a browser toolbar they had, but disbanded the service for some reason. I'm not sure if they've replaced that functionality

I think PayPal used to do it through a browser toolbar they had, but disbanded the service for some reason. I'm not sure if they've replaced that functionality in some other product. With Netspend, you get one of their physical cards, but you also get a login for their site where you can create as many virtual cards as you want. The virtual cards use the balance from the main card, and you can shut off each virtual card whenever you feel like it.