I am unsure what the nit defender is. I assume that it is just some extra bundled software from the manufacturer that you bought it from. All you need to run the graphics card with is the regular ATI catalyst drivers. You should be able to uninstall it I would imagine, just make sure you have the drivers off to the side so you can re-install it if needed.
I purchased the Sapphire version and I didn't get anything called nit defender to my knowledge unless it is hidden somewhere very well.
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