How to Prevent SPAM without CAPTCHAs or a Centrally managed system (e.g. akismet)

Question

Has anyone been able to successfully prevent spam on their site without placing a burden on your visitor (e.g. CAPTCHA) and without using a centralized spam reporting system (e.g. Akismet)

I've found this & it looks promising, but doesn't contain detailed deployment instructions.

I want to present my web forms without burdening my users with CAPTCHA like technologies, but also actively automate preventing spam.

There doesn't seem to exist a detailed instruction/tutorial on how to implement such a technology.

Disclaimer

Also, I realize there no silver bullet appropriate to preventing spam. But if simply putting in place a non-invasive (invisible to user) prevention system that blocks 95+ % of spam, it would be worth the effort to deploy.

Answer 1

I basically use one trick on my site to prevent Spam and it works great (at least until spambot programmers will read this post ;) ).

Code is like this:

In the script that builds the site which contains the form, I implemented:

$_SESSION['lastSiteId'] = 'something Unique';
$_SESSION['lastSiteRequest'] = time();

The script that contains the logic to write the comments to a database contains this:

if($_SESSION['lastSiteId'] == 'something Unique' 
   && $_SESSION['lastSiteRequest'] + 5 < time()){

    insertComment();
}else{
    echo "Please read the article before posting a comment";
}

Remember this is pseudocode to give you the idea. You have to implement it all alone in the end... ;)

All it does is checking if more than 5 seconds have passed between redering the form and sending a POST Request.

Be warned that spambot engineers are not sleeping. Bets are, that spambots can wait a few seconds before posting unwanted input if the programmer wants it that way. Question would be: How much spam messages can be send if the Spammer have to wait 5 secs between the requests? See, maybe this IS the final solution to Spam prevention.

Combining time tests with javascript tests (if possible and wanted) plus prefilled/unfilled hidden fields tricks, you should be save from spam a few years from now on.