You can use the option allowing only registered users to post comments if what you want is to prevent "visitors" from browsing.
But it sounds like you want to hide these comments from the back end comments tab. Is that correct. If so, that is not possible. As well, I can think of no good reason for doing so.
Comments
But it sounds like you want to hide these comments from the back end comments tab. Is that correct. If so, that is not possible. As well, I can think of no good reason for doing so.