I believe that saying goes for even Linux Systems. The Firewall is the most important tool you’ll need to avoid intrusion, attacks, and break-ins.
In late 2011 while I was employed for a Shared Hosting company I fell in love with CSF (https://configserver.com/cp/csf.html).
CSF can be configured on almost anything with or without cPanel. I will provide some more information as I update this article. Be safe!