Website Firewall like Sucuri

I have a question regarding the way sucuri protects it own website. Here is the link btw: https://sucuri.net/wp-admin

How do they do that?

I kind of want to achieve the same result for my own site and I’m currently looking into the best way to achieve that. Plugins to use etc etc.

So if you guys have any advice and/or feedback regarding this, do tell!