Simple question that blocks most spambots (and paid robots) by making them answer a common sense question

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BuddyPress - Validate XProfile data with PCRE regular expressions.

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Email Address Obfuscation prevents email harvesting by hiding email address appearing in your pages, while remaining visible to your site visitors.

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Comprehensive spam protection for WordPress registration, login, comments, and contact forms.

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Add Hashcash spam protection to Contact Form 7.

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Zero Spam makes blocking spam comments and registrations easy.

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Easy-to-use tool to get rid of spam attacking your website AntiSpamLight is developed to help you to forget about annoying spam bots! No more spam and …

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Performs a simple but very effective test on all incoming trackbacks in order to stop trackback spam.

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