Even i am in the same boat. I also installed andriod 4.3 but KNOX came with the pack. Now whenever I try to use SuperU or Root application, Knox gives me an error.
If I click on Knox app, it asks me whether to install and create an account. Hence, I am sure, Knox is not installed yet in my device, but still I get error - "Unauthorized access to a secured area has been blocked. Tap to learn more." I believe this is fully related to the new security app "KNOX" from samsung that was loaded during the update.
Can anyone give some hint how to remove Knox or regain root access?