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 21,867 websites that are WP Captcha Customers. We know of 11,599 live websites using WP Captcha and an additional 10,268 sites that used WP Captcha historically and 3,747 websites in the United States.
Get a list of 21,867 websites using WP Captcha which includes location information, hosting data, contact details, 11,599 currently live websites and an additional 4,591 domains that redirect to sites in this list. 10,268 sites that used this technology previouslyand 3,747 websites in the United States currently using WP Captcha.
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