Hidden Text Box For Anti-Spam

I read an article about using a hidden text box on a form to stop spam bots.  Since the bots usually enter all of the fields automatically, placing a hidden field could stop them.  This would be by checking to see if something is entered in it before the insert.

I already have an existing formview.  I've added a hidden text box and binded it to a new field I created in the database called Hidden. 
What is the SQL to not insert if the text box is not null?  I've tried all kind of variations and I can't get the form to insert.
InsertCommand="INSERT INTO [database2].[Guestbook] ([Date_Entered], [Location], [Name], [Comments], [Approval] , [Hidden]     ) VALUES (@Date_Entered, @Location, @Name, @Comments, @Approval, @Hidden )
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