Plugin for using reCAPTCHA in WordPress.
http://wordpress.org/plugins/wp-recaptcha
Widgets · CAPTCHA · WordPress Plugins
Get access to data on 83,770 websites that are WP reCAPTCHA Customers. We know of 6,711 live websites using WP reCAPTCHA and an additional 77,059 sites that used WP reCAPTCHA historically and 3,730 websites in the United States.
Get a list of 83,770 websites using WP reCAPTCHA which includes location information, hosting data, contact details, 6,711 currently live websites and an additional 2,501 domains that redirect to sites in this list. 77,059 sites that used this technology previously and 3,730 websites in the United States currently using WP reCAPTCHA.