I searched https://cs.stackexchange.com/ for "Halting problem" and got redirected to a captcha. I'm not even modifying anything, just searching. What is prompting this?

1 Answer 1


All anonymous use of the search engine requires passing a captcha.

If you log in to the site the captcha disappears.

Searching takes resources too, and apparently some robots have been trying to use the search engine a lot lately. The captcha is there to limit that abuse.

  • Does this affect anonymous users with the cookie?
    – Tim
    Apr 16, 2015 at 15:34
  • @Tim: I don't know. To get that cookie I'd have to create a duff question somewhere that accepts unregistered account questions ("post as a guest"). As such it could well be that using search with such a cookie doesn't require a captcha to be passed first. Apr 16, 2015 at 15:52

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