This plugin will add a client side generated checkbox to your comment form asking users to confirm that they are not a spammer. It is a lot less trouble to click a box than it is to enter a captcha and because the box is genereated via client side javascript that bots cannot see, it should stop 99% of all automated spam bots.

A check is made that the checkbox has been checked before the comment is submitted so there’s no chance that a comment will be lost if it’s being submitted by legitimate human user.

This plugin really very usefully and accurate protected from spam bots.

Setelah hampir 1 tahun saya menggunakan plugin ini. Hasilnya cukup memuaskan, sangat ampuh mencegah spam-robot. Saya merekomendasikan Anda untuk mencoba.

Reference: Growmap Anti Spambot Plugin 

Download Plugin: Growmap Anti Spambot Plugin