I’ve added a new layer of comment spam protection to this site: a math-based captcha. Now when you leave a comment, you’ll have to prove you’re human by answering a simple math question, such as 3 + 7.
Some generous German fellow created an easy-to-install WordPress plugin, and it seems to be working well (and erroring out gracefully).
What do you think? I prefer it to the usual type-the-messed-up-word-in-a-box, because it’s easier and more reliable (I can’t read the text in the box one out of five times). I’ve been using Akismet for at least a year, but the volume of spam messages means that I can’t easily scan for or rescue false positives.
Of course, if this form of comment spam prevention gets popular, then the spammers will just program around it. I’ll see how effective it is, and if nobody hates it, will keep it for the time being.
UPDATE: Twelve hours later, and only three new messages in the spam bucket, where I’d usually have 300. Three isn’t zero, though, and that suggests that this captcha won’t foil the spammers for long.
DarrenBarefoot.com 
I’ve been using Bad Behavior for about four months or so now, and it’s very effective in conjunction with Akismet.
http://www.bad-behavior.ioerror.us/
I saw one a few weeks ago that asks basic knowledge questions.
“Last name of the first US president”
“First Month of the Year”
“Current Year”
“First word of the title of this Post”
Personally I would prefer something that would give painful electrical feedback to the spammers but the possibility of false positives in a deterrent, at least with the amount of pain I’d want.
Roll up the website to win… I’m suddenly reminded of the skill-testing questions that are commonplace in Canadian lotteries.
I’m just checking to see if I still get stuck as spam.
I recall once seeing a concept that had something like a 3×3 grid, with 8 photos of cats, and one of something else, and the idea was you click the one that isn’t a cat. There’s something software can’t easily do .. yet.
Math, on the other hand, is one thing all computers definitely can do. I’m afraid it might be easily circumvented.
I’m using Pivot’s Hashcash for spam protection at the moment. Geeks keep telling me that a simple trick like Hashcash that requires no user-unfriendly captcha or false-positive-happy bayes system would be broken by spammers so why bother? Well it’s been there for a year now and I can still be confident the handful of spam comments that made it through were added by “real people”. Sure, it’ll get broken eventually, but in the meantime it’s by far the most effective and simplest solution.
sorry, just testing your captcha
Just giving your CAPTCHA a try. Wondering if there is a non-blog version of it – will follow the link you provided after this and find out. Cheers.
Hey looks like you are not using CAPTCHA any more.
We are looking for easy text-based real simple math CAPTCHA for lite level form mail spam protection and for accessibility. Not audio.
Are there any popular scripts that fit this description, anyone? I have been on this since morning, and all I can find are image-based math CAPTCHAS and nothing accessible.