From https://support.google.com/websearch/answer/86640

You may see "Our systems have detected unusual traffic from your computer network" if Google detects that a computer or phone on your network may be sending automated traffic to Google.

Automated traffic includes:

Sending searches from a robot, computer program, automated service, or search scraper Using software that sends searches to Google to see how a website or webpage ranks on Google

When this happens in Google Books, what are some possible criterions that Google Books or similar sites can use to detect that a compute may be sending automated traffic to their sites?

  • Your IP address is probably the major criteria. Things like User-Agent, lack of cookies/session id, etc, are probably secondary criteria. Using torproject.org may help – user5676 Nov 22 '14 at 16:31
  • @barrycarter, I doubt it. Tor exit nodes get blocked very quickly by Google. – Nemo Apr 20 '15 at 22:42

Google uses complex anomaly detection systems, which are getting popularised with the NoCaptcha ReCaptcha.

Everything started with a mere counting of accesses, of course. You can have fun looking for more Google stuff.

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