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145

answers:

1
+3  Q: 

StackOverflow CAPTCHA Triggers

Normally whenever a CAPTCHA might be needed I always present it to the user apriori but the StackOverflow approach is much better, it only shows me the CAPTCHA when it thinks I might be a bot.

I'm interesting in learning the requirements and how I could implement a similar system on my projects. What are the actions that make SO believe I'm a bot? Is there any time frame for doing such actions? Does such a system require any particular database design?

+3  A: 

I would log time between actions, and if under (for example) 10 seconds then require a CAPTCHA to continue.

alex  2009-04-29 04:01:26
Doesn't SO just make you wait in that scenario?
Mark  2009-04-29 04:04:29
It does for requesting and sending comments, but editing a post again too quickly will trigger the CAPTCHA.
alex  2009-04-29 04:14:12

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