web form spam continued . . .

HI, I have tried adding a hidden field to my web form to help reduce spam. I am not sure what I tried will work and do I need to and how do I add some code to specify do not process form if this field is filled in?

Here is what I tried so far and any help would be awesome - Thanks Jim

<!--- rest of form above--->

<div style="display:none; visibility:hidden;">

     <label for="contact_email">Please leave this field blank:</label>

     <cfinput type="text" name="contact_email">

</div>

<div class="register">             
            <cfinput type="submit" name="submit" value="Register">

            <cfinput type="reset" name="Reset " value="Reset Form">         

</div>

               </fieldset>

</cfform>