Google finally rolled out the invisible reCAPTCHA! No more captcha challenges, no more proving that I’m made from flesh and bone and not from a few lines of code! Invisible reCAPTCHA, is powered by an advanced risk analysis system. If the system is sure that visitor is a human, no captcha will be shown, which is actually good for the business and may improve the conversion ratio. If you ask me how, the answer is simple, it saves time! On the other hand, if bot is detected the captcha box will pop up and kill the bot along with the evil dev who dared to code that nasty creature to leave crap all over the net.
For more info go here: https://www.google.com/recaptcha/admin#list