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What can be done to prevent spam in forums?

Are there ways other than CAPTCHAs for web applications like pastie.org or p.ramaze.net ? CAPTCHA take too much time for a little pasta for my taste.

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You can try Honeypot CAPTCHAs . Essentially, you hide some form fields using CSS. Your users will never fill in the fields because they do not see them, but spam bots that do not support CSS will fill them. On the server side, you simply ignore comments / inserts / etc. that fill this field.

In addition to honeypots, you can use timestamps and one-time tokens to stop replay attacks. Here's a discussion of combining the two methods .

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Personally in my blog I received a lot of spam from bots. After analyzing how spam looked, I did some quick regular expression to discover things like a message full of links, or cases where the subject, comment, and name fields were filled with the same text. I show a nice message if the message is blocked. Since I used this technique, I went from hundreds of spam comments per week to almost zero. I assume that I'm trying to say, it analyzes what kind of spam traffic you get, and see if there is an easy way to cut it out, simply using simple analysis, and not resorting to something like captcha.

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I have successfully used hashcash before.

This requires a javascript-enabled browser and a delay of several seconds (configurable), but has the advantage that it does not add interface complexity.

While hashcash does not prevent spam per se, it requires the spammer to spend time calculating javascript hashes, which in turn requires the spammer to enable javascript (which is quite rare) and that it cannot do more than some spam per minute

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You can try Akismet . It is very good at blocking spam, it can be free (depending on your use) and has an API for numerous web applications.

Your two are not listed, so it will take some work to get them to work with them. Sources based on pastie.org? If so, there is a rails API for Akismet.

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from wikipedia

The CAPTCHA system is a tool that automatically generates new problems that:

* Current software is unable to solve accurately. * Most humans can solve. * Does not rely on the type of CAPTCHA being new to the attacker.

I myself am not good at Captchas (at least based on images), and for me it looks like current implementations don't fill out the “spec” above. Many widely used implementations can actually be solved with software. I, like most people, and I can’t solve them ... (subjectively know)

I would probably try to implement a system in which users can flag material as spam, which I would delete. Yes, spam will be visible, but not for long, without entering the administrator himself.

Think about it, the reputation and voting system here at SO quite effectively reduces the impact of spam when questions are closed and voted down => lover visibility

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Check out defensio.com. It uses Bayesian filtering (for example, filters for letters). It is quite effective. This is a free web service.

Disclaimer: worked there in the past.

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How about something like Phil Haacks an invisible captcha ?

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