How do you protect your e-book? What can I do to prevent one person buying it and ping it...?

A very good product for this is NitroPDF, you can download a free trial at nitropdf.com. With NitroPDF you have a number of other tools that really help to improve the quality of the published work. Sybrex is a company that has a number of helpful tools that you can try before you buy: sybrex.com.