Stop spam without captcha

Question

I want to stop spammers from using my site. But I find CAPTCHA very annoying. I am not just talking about the \"type the text\" type, but anything that requires the user to

Answer 1

If you're looking for a .NET solution, the Ajax Control Toolkit has a control named NoBot.

NoBot is a control that attempts to provide CAPTCHA-like bot/spam prevention without requiring any user interaction. NoBot has the benefit of being completely invisible. NoBot is probably most relevant for low-traffic sites where blog/comment spam is a problem and 100% effectiveness is not required.

NoBot employs a few different anti-bot techniques:

• Forcing the client's browser to perform a configurable JavaScript calculation and verifying the result as part of the postback. (Ex: the calculation may be a simple numeric one, or may also involve the DOM for added assurance that a browser is involved)
• Enforcing a configurable delay between when a form is requested and when it can be posted back. (Ex: a human is unlikely to complete a form in less than two seconds)
• Enforcing a configurable limit to the number of acceptable requests per IP address per unit of time. (Ex: a human is unlikely to submit the same form more than five times in one minute)

More discussion and demonstration at this blogpost by Jacques-Louis Chereau on NoBot.

<ajaxToolkit:NoBot
  ID="NoBot2"
  runat="server"
  OnGenerateChallengeAndResponse="CustomChallengeResponse"
  ResponseMinimumDelaySeconds="2"
  CutoffWindowSeconds="60"
  CutoffMaximumInstances="5" />

Answer 2

I realize this is a rather old post, however, I came across an interesting solution called the "honey-pot captcha" that is easy to implement and doesn't require javascript:

Provide a hidden text box!

• Most spambots will gladly complete the hidden text box allowing you to politely ignore them.
• Most of your users will never even know the difference.

To prevent a user with a screen reader from falling into your trap simply label the text box "If you are human, leave blank" or something to that affect.

Tada! Non-intrusive spam-blocking! Here is the article:

http://www.campaignmonitor.com/blog/post/3817/stopping-spambots-with-two-simple-captcha-alternatives

Answer 3

Integrate the Akismet API to automatically filter your users' posts.