John Dalesandro

Most spam filters make your visitors do the work by solving captchas, clicking image grids, or proving they are human before they can leave a comment. Analytical Spam Filter takes a different approach. It analyzes how a submission behaves and blocks spam automatically, with no friction for legitimate visitors.
Key Features
<ul>
<li>No captchas</li>
<li>No API keys</li>
<li>No third-party services</li>
<li>Privacy-friendly design</li>
<li>Behavioral spam detection</li>
<li>IP reputation tracking</li>
<li>Content fingerprinting</li>
<li>Cache-compatible operation</li>
</ul>
Install it, activate it, and it starts working.
Spam is identified by observing behaviors that real visitors naturally exhibit. People take time to read before typing, interact with the page, and use a real browser. Bots often skip those signals. The plugin uses those differences to distinguish legitimate submissions from automated spam without interrupting the user experience.
The plugin uses multiple independent detection techniques on every submission. A bot that bypasses one check is likely to be caught by another. This layered approach improves effectiveness over time. Once a spammer’s IP address or message content has been identified, future attempts can be blocked more quickly. Visitors with a previously approved comment are never flagged, regardless of the spam history associated with their IP address.
No visitor data is sent to external spam services, and no account registration or API configuration is required.
All field names added by the plugin are randomized during installation and can be regenerated at any time. This helps prevent bots from targeting the plugin based on known source code signatures. The plugin is compatible with caching plugins when Cache Compatibility is enabled.
The plugin blocks spam submitted through the default WordPress comment form only. It is also automatically compatible with the Micro Contact Form plugin.
<h4>Blocking Methods</h4>
<ul>
<li>Timestamp Blocking — Records when the page loaded and when the form was submitted. Submissions that arrive too quickly to have genuinely read the page, or after the token has expired, are blocked.</li>
<li>Duration Blocking — Measures how long the visitor actively spent filling out the form. Bots fill forms almost instantly. Requires Cache Compatibility to be enabled.</li>
<li>IP Blocking — Remembers which IP addresses have been blocked before. Once an address reaches the configured threshold, future submissions are flagged without running the remaining checks. IP addresses with a previously approved comment are never flagged.</li>
<li>Content Blocking — Remembers the content of blocked spam. If the same message appears again from a different IP address, it is flagged immediately. Content that matches a previously approved comment is excluded from the spam history.</li>
<li>Honeypot — Adds a hidden field that legitimate visitors never see or interact with. Bots that fill every available field are caught. Submissions where the field is missing entirely are also flagged.</li>
<li>Automated Client Detection — Blocks submissions from automated tools that do not identify themselves as a real browser. Legitimate visitors send this information automatically.</li>
<li>Referer Check — Blocks submissions that did not originate from a page on your own site.</li>
<li>URL / Domain Blocking — Flags submissions containing more URLs or domain names than the configured limit. Spam comments frequently contain multiple links.</li>
<li>JavaScript Check — When Timestamp or Duration Blocking is active, the plugin can determine whether JavaScript ran when the form loaded. Bots that skip JavaScript are caught automatically.</li>
<li>Randomized Field Names — Hidden field names are randomized during installation and can be regenerated at any time from the settings page, so bots cannot target the plugin based on known field names.</li>
<li>Trackback Blocking — Optionally block all trackbacks, which are a common source of spam.</li>
<li>Pingback Blocking — Optionally block all pingbacks, which are a common source of spam.</li>
</ul>
<h4>General Options</h4>
<ul>
<li>Send email notifications for blocked spam, valid submissions, or all submissions</li>
<li>Configurable email rate limit to prevent inbox flooding during attacks</li>
<li>Add spam to the WordPress spam queue, or block and reject it immediately</li>
<li>Optionally show rejection reasons to the submitter</li>
<li>Enable Cache Compatibility for caching plugin support and duration blocking</li>
<li>Regenerate security keys at any time from the settings page</li>
</ul>

Analytical Spam Filter

Stop spam without making your visitors prove they're human. No captchas, no accounts, and no external services required.

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