Radek Mezulanik

This plugin:
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Add 3 hidden fields to Registration form and to Comments form, that only robots can see. Plus you can choose to add validation checkbox to forms.
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Add to .htaccess file direct access protection for comments file.
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Check time user spent on page and time when user send a form.
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Disable trackbacks for past and future posts.
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Additionally you can choose to add validation checkbox to forms.

Antispam Revolution

Three way antispam protection for registration and comment forms.

joe031102

Chinese Comment Spam Protection asks the visitor making the comment to key in/copy a simple chinese word. This is intended to prove that the visitor is a human being but a spam robot.
Example: 成长？路 请输入“之”字
This plugin does not require JavaScript or cookies. The result of the question is being passed via a hidden field. The result is being compared with the value entered by the visitor.
Please visit <a href="http://iibetter.com/12198.html" title="Chinese Comment Spam Protection" rel="nofollow ugc">the official website</a> for further details and the latest information on this plugin.

Chinese Comment Spam Protection

Asks the visitor making the comment to key in the disappeared chinese word. This is intended to prove that the visitor is a human being but a spam rob …

Antispam Revolution vs Chinese Comment Spam Protection