If you take payments on your website, be sure to protect your checkout page with a Captcha. Captcha challenges the user with options like selecting certain images or typing in a code to make sure they are real instead of a bot. This will prevent hackers from using your website to test thousands of stolen credit card numbers on your site to see which have been closed and which are still usable. They can rack up thousands of dollars in authorization attempts as well as chargebacks for charges on cards that have not been closed.
You as the merchant are responsible for all transactions/transaction attempts processed on your merchant account and are responsible for all fees resulting from this kind of hack so make sure to protect yourself.
There are many different types of Captcha options to choose from so you can talk to your website developer about the best option for you.