Prove that the visitor is a human being and not a spam robot.
https://wordpress.org/plugins/wp-captcha
Widgets · WordPress Plugins
Get access to data on 22,031 websites that are WP Captcha Customers. We know of 11,511 live websites using WP Captcha and an additional 10,520 sites that used WP Captcha historically and 3,736 websites in the United States.
Get a list of 22,031 websites using WP Captcha which includes location information, hosting data, contact details, 11,511 currently live websites and an additional 4,545 domains that redirect to sites in this list. 10,520 sites that used this technology previouslyand 3,736 websites in the United States currently using WP Captcha.
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