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 22,086 websites that are WP Captcha Customers. We know of 11,638 live websites using WP Captcha and an additional 10,448 sites that used WP Captcha historically and 3,804 websites in the United States.
Get a list of 22,086 websites using WP Captcha which includes location information, hosting data, contact details, 11,638 currently live websites and an additional 4,824 domains that redirect to sites in this list. 10,448 sites that used this technology previouslyand 3,804 websites in the United States currently using WP Captcha.
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