If you use a public computer, or a computer that is not yours, to buy something on Amazon, you should make sure to log out when you are done. This is especially important since Amazon allows you to make purchases without re-entering credit card information. The only problem is that, unlike most websites that contain personal information, Amazon does not have a "log out" button. So what you need to look for instead is the link near the top of the page that says "If you're not YOUR NAME, click here". If you don't see the link on the page you are on, go to the Amazon home page as this link is always shown there. Clicking on this link will effectively log you out on Amazon.