Using a honey pot or honey trap, spam bots are lured into a trap and get locked out. The honeypot is a set of multiple visually hidden fields, that are the bait. Human visitors can't see the fields and thus won't fill or change them – most spam bots will. The plugin checks even more factors in the background to separate users from spam bots even more effectively.
If a user is classified as a spam bot by mistake, he just needs to fill the default captcha or calculation. You won't ever loose form data.
RockSolid Antispam protects your site completely invisible. Only in exceptional cases the default CAPTCHA is used as a fallback to sort false positives out.
The plugin uses the tried and tested honeypot method to lure spam bots with visually hidden fields and offers effective protection from annoying junk mails.
Don't stop your users from sending your form by making them solve calculations or CAPTCHAs, which meaning many people don't really understand.