Spam protection with obscurity is different from security through obscurity. Spam protection through obscurity is fairly prevalent and reasonable.

A better technique is one where even if the spammers know what your countermeasures are, they still can't spam you.

Good luck! :)

Unless you're taking a blood sample from every user, you are going to have spam that you can't catch.

If a robot makes a meaningful contribution to your website / service, do you really care if they are a robot?

If you could tell which comments are insightful / relevant / interesting / unique it wouldn't matter which ones were produced by humans and which ones by algorithms.

Likewise humans can often create spam by hand - daft comments / contributions that hurt your site but come from legitimate humans.

The assumption with any kind of collaborative filtering is that the opinions of many people produce a better result when combined than the opinions of one person. If you are allowing machines to vote then you're letting one person have an arbitrary number of votes, which totally breaks the model.

How would blood samples even help? We're talking about excluding content, not people.

It's a certainty that the spam you can't define is the spam you can't catch. The "I know it when I see it" test doesn't scale.

That's the only way you're going to be able to ensure that everyone interacting with your site is a human. (It's preferable if you take a blood sample on every interaction, just in case.)

Yes, but didn't they wait until they had a very established community? And they're not really a technology play--not to discount their technilogy--but their success seems to be all about their community.

I use DuckDuckGo almost exclusively for web searching, but admit I hadn't really thought of DDG as a technology play, either.

To date, I've concentrated on community as well, although doing so in my case is arguably more intertwined with technology. In any case, I wasn't making reference to DDG, just adding more color to the reddit decision.