I personally experinced high CPU load if I enable the "File Change Detection" feature in this plugin. Other than that, I never seen any significant perfomance issue.
Thanks for that, Handoko!
I, too experienced high CPU load on my dedicated server, and could not figure it out. iThemes Security ought to make that very clear on the checkbox for File Change Detection.
It was so bad I had to reboot the server a few times to unfreeze it, so I could work on it some more.
It was a real pain in the butt, finding the source of the problem, and I wasted a lot of time on it. Should I have been able to figure it out quicker? Probably, but they really need to make the risk of that feature clearer.
So, thanks for the hint!