

CAPTCHA + Calculation (As Opposed to One or the Other) - danielrm26
http://danielmiessler.com/blog/captcha-calculation-excellent-human-check

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RiderOfGiraffes
Interesting, but I add this data point ...

On a site I manage I ask people to enter 4 plus nine (in digits). Recently
I've had the following answers: thiteen, 13, tirteen, thirten, thurteen, and
11.

Yes. 11.

The question is, if someone can't add 4 and 9 do you want their opinion?

