After installing patch SUPEE-9767 the "Enable Form Key Validation On Checkout" warning appeared and from the link provided in that warning I was able to enable Form Key Validation.
But, after having some issues in the checkout process I would like to try to disable it and check if everything comes back to normal.
The big problem here is that I cannot find where the option is in the admin menu.
I seem to recall it was in:
System > Configuration > Advanced > Security > Enable Form Key Validation On Checkout
But if it was there, now it has disappeared. Do I recall it wrong or what might be the issue?