Plugin for using reCAPTCHA in WordPress.
http://wordpress.org/plugins/wp-recaptcha
Widgets · CAPTCHA · WordPress Plugins
Get access to data on 83,629 websites that are WP reCAPTCHA Customers. We know of 7,403 live websites using WP reCAPTCHA and an additional 76,226 sites that used WP reCAPTCHA historically and 4,097 websites in the United States.
Get a list of 83,629 websites using WP reCAPTCHA which includes location information, hosting data, contact details, 7,403 currently live websites and an additional 2,720 domains that redirect to sites in this list. 76,226 sites that used this technology previously and 4,097 websites in the United States currently using WP reCAPTCHA.