Google knows your searches, and I am pretty sure google knows every site you visit, via google analytics, which most sites run. Combine this with browser finge

Google knows your searches, and I am pretty sure google knows every site you visit, via google analytics, which most sites run. Combine this with browser fingerprinting (your browser's fingerprint is incredibly unique), and the fact that you probably have a google account. There is a high probability they know who you are. From your history they can determine if you're human or not.