Anti-Captcha is a transparent spam solution that does not require any end-user interaction.

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Anti-Captcha is a transparent spam solution that does not require any end-user interaction. 
It is based on a nonce key, which is dynamically inserted using randomly generated (and obfuscated) javascript.
The aim of this plugin is to prevent automated attacks (by bots) on the following WordPress actions:
<ul>
<li>Posting comments</li>
<li>Registering for a new account</li>
<li>Requesting a lost password</li>
</ul>
When a comment is posted without a valid Anti-Captcha token, it shall be instantly marked as spam. This way, you can always manually approve this comment in hindsight if it appeared to be sincere.

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