3D objects-based CAPTCHA to get rid of spam in comments.
Unpack archive with plugin into "wp-content/plugins" folder on your WP-based site/blog. You will see "ironclad-captcha" folder with several files there. Log into WP control panel and go to Plugins section. Find "Ironclad CAPTCHA" string in the list of available plugins and click Activate next to it. Plugin is installed now! Don't forget to configure it.