Cloudflare is very famous in against DDoS attacks. Their by-product is the IP address of the protected sites are hidden if the owner of the protected sites are setting it correctly. However, it is not very easy to set it correctly when the owners do not fully understand well the services that Cloudflare is provided.
Many website owners choose to use Cloudflare services including criminals. There are a lot of methods to resolve the IP address of the websites that behind Cloudflare protection, such as CrimeFlare. Almost all these methods are targeted to the mis-configuration of Cloudflare. Some of the methods do not work as Cloudflare has been fixed the problem long time ago.
Recently, there is a new method to resolve the IP address of the websites that behind Cloudflare, that is Cloudflare IP resolver. However, if the webmaster or sysadmin is clever enough, this method is also failed.
No matter how, this new method is also a killer to Cloudflare for sure.
Finally, when you think that your system is very very secure, your system will be very danger.
That's all! See you.