John Dalesandro

The Analytical Spam Filter plugin for WordPress blocks comment, trackback, and pingback spam. It uses multiple spam detection methods without challenging the user with obstacles such as captchas, math problems, etc. and it does not rely on external services or APIs. This is a low overhead plugin that begins blocking spam as soon as it is activated. It is compatible with caching plugins as long as the user has JavaScript enabled. The plugin blocks spam submitted through the default WordPress comment form only.
Logic is used to identify spam comment submissions. No user interaction is required. The spam blocking mechanisms work transparently behind the scenes. Most visitors will require longer than a few seconds to read a post and add a meaningful comment so any comments submitted within a short time threshold are identified as spam. Comments containing a large number of links are flagged as spam. The plugin uses an encrypted code and a honeypot to filter robotic submissions. All field names added by the plugin are randomized to prevent detection based on a source code signatures.
Configuration options include:
<ul>
<li>Enable Cache Compatibility (requires JavaScript)</li>
<li>Add spam to WordPress queue or block completely</li>
<li>Send diagnostic information to site administrator</li>
<li>Automatically compatible with the Micro Contact Form plugin to block spam messages.</li>
</ul>
Blocking options include:
<ul>
<li>Honeypot Trap</li>
<li>Randomized Internal Field Names</li>
<li>Timestamps (minimum and maximum entry time)</li>
<li>Aggressively check for excessive URLs</li>
<li>Check if JavaScript is enabled</li>
<li>Automatically block repeated spam from IP</li>
<li>Automatically block repeated spam based on content</li>
<li>Require User Agent string</li>
<li>Require Referer</li>
<li>Block Trackbacks</li>
<li>Block Pingbacks</li>
</ul>

Analytical Spam Filter

Block WordPress comment spam, trackback spam, and pingback spam through intelligent analytics instead of interactive challenge response tests.

Matt Lowe

Unspam by Squelch Design is the simplest <a href="http://squelchdesign.com/wordpress-plugin-squelch-unspam/" rel="nofollow ugc">WordPress anti-spam plugin</a> you can find for reducing your comment spam problem. Once installed there’s nothing 
to configure, and nothing changes to your visitors: No captcha or silly games. Once installed 
the plugin will simply randomize the names of the fields in the comments form on your blog and reject comments that are sent to the 
standard WordPress field names, or where bots have blindly submitted data to the honeypot fields.
What this means for spammers is that they have to do quite a lot more work to send spam to your website. It may also make sending 
spam to your website unreliable as changes to your theme may upset their spam submission tools. Or they may have to resort to using 
humans to send spam to your website (not much I can do about that I’m afraid) which will cost them more money.
Currently implemented:
<ul>
<li>Names of fields are randomized every night at 12:00,</li>
<li>Submissions to the standard WordPress field names are automatically deleted,</li>
<li>Honeypot fields added to comments form,</li>
<li>WooCommerce support.</li>
</ul>
Additional (planned) features:
<ul>
<li>Contact Form 7 integration</li>
<li>Statistical collection,</li>
<li>Automated blocking of persistent IPs,</li>
<li>Opt-in centralized collection of comment spam and statistics for additional research.</li>
</ul>

Squelch Unspam

Unspam makes it harder for spammers to automatedly send spam to your blog by changing the names of the fields in the comment forms.

Analytical Spam Filter vs Squelch Unspam