Site being Hacked

My site is being hit with a certain IP address that is adding <iframe lines to my code.

What do I do to prevent this IP from getting into my site?

I have manually taken out the code, but he/she keeps doing it.

Thanks for any help.

My site is adult orientated. Do not click if you are offended by mature content.
<url removed>

Hello ..

Please purchase a license for SmartFTP because it is not free for commercial use.
Thank you
https://www.smartftp.com/buy.php

Regards,
Mat