Non member spam in feedback module - How to avoid?

How can i avoid spam in the feedback module from non members?

How can i (in general) control the activity of non member? I was surprised that there in no button in the feedback module except for auto approve of content.

See my response to another post here . The default Feedback module is basic and missing some necessary features. You can check out the Advanced Feedback module with more robust features such as Captcha integration and Membership Level control.