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Possible Duplicate:
How often do captchas appear?

Occasionally, when I ask a question on Stack Overflow, I'll see this page wanting to verify whether or not I'm human.

I'm trying to figure out what I am doing that looks suspiciously non-human. How is this page triggered?

(Ironically, when I posted this question, it asked me to do the CAPTCHA.)

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marked as duplicate by studiohack, Chris Frederick, kiamlaluno, Dori Nov 3 '11 at 1:57

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Good try, robot. – Pëkka Nov 2 '11 at 15:54
I'm pretty sure that this won't get an (official) answer. Documenting what makes the system suspicious would make it far too easy to game the system. – Joachim Sauer Nov 2 '11 at 15:58
I agreed with @Joachim, until I found this question. Its a couple of years old, but will give you an idea of how it works. – ughoavgfhw Nov 2 '11 at 16:00
What triggers the CAPTCHA for me every time is if I paste a question or answer into the edit box and then hit "Post" straight away. – ChrisF Nov 2 '11 at 16:11
@JoachimSauer If documenting their security measures would make them easy to game, then they have poor security measures, i.e. security through obscurity. – Peter Olson Nov 2 '11 at 17:16
I strongly believe in Kerckhoff's Principle, but there's a difference between making something secure and making it harder for spam bots to waste everybody's time. – balpha Nov 2 '11 at 17:26

In my experience, that page tends to appear when I write my answer in Notepad, for example, then paste the answer into the answer box and then immediately click Post Your Answer.

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+1 Just because your name is Peter O., like me. – Peter Olson Nov 2 '11 at 19:54

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