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.

Frank Bueltge

Inpsyde GmbH

Eric Teubert

Simple antispam solution. Scrambles a word and pieces it together automatically via JavaScript. Users with JavaScript enabled won’t notice anything. Those who have JavaScript disabled have to type the word into a textfield. This plugin won’t help against a targeted spam attack but should prevent a lot of random spam.
No remote service needed. Does not send or retrieve data from third party services.
<h4>Bugs, technical hints or contribute</h4>
Please give us feedback, contribute and file technical bugs on <a href="https://github.com/inpsyde/inpsyde-antispam" rel="nofollow ugc">GitHub Repo</a>.
Made by <a href="http://inpsyde.com" rel="nofollow ugc">Inpsyde</a> · We love WordPress
Have a look at the premium plugins in our <a href="http://marketpress.com" rel="nofollow ugc">market</a>.

Inpsyde AntiSpam

Simple antispam solution with the magic of javascript

Antispam Revolution vs Inpsyde AntiSpam