Google launched the "Invisible reCAPTCHA"

Google launched "Invisible reCAPTCHA" a service that functions as a background bot-sniffer--without any action of human to do anything.  (According to Google, the Beta version was launched in last November.)

With commitment to make the Internet a more reliable and happy place,  Google has taken this step much effectively by turning the security step invisible.

Earlier, the regular practice was to type or transcribe letters or numbers as CAPTCHA in a small box to prove that you're not a robot while doing something online like opening a new email account.

This version of Google is called reCAPTCHA, while the previous was like checking the box that says "I'm not a robot." But now you may not face the tyranny of clicking that box.

“Powering these advances is a combination of machine learning and advanced risk analysis that adapt to new and emerging threats,” Google says.

Whether a website implements the new, invisible reCAPTCHA or just the box-checking version, Google says that if they are of the opinion that something's fishy, user will have to confront more challenges.

“ReCAPTCHA is one of the most popular, if not the most popular, CAPTCHA mechanism on the internet today,” Shuman Ghosemajumdar, the Chief Technolgy Officer at Shape Security says of the free service. 
"Google in general—and this is certainly a philosophy that we adhered to when I was there—believed that anything that is good for the internet, is good for Google.”
The invisible service is primarily  “to improve the user experience across the web.” he says.
The new invisibility systems takes care of factors like how a user navigates the mouse around, CTO says.
 “Google also has a history of information that’s associated with that particular IP address,” Shuman says and further points out that if the user is also logged into a Google account, the company will be able to know even more about the dos and don'ts of normal activity.

“It was the worst of all possible worlds, in terms of most humans experiencing something that was very frustrating, and most bots not encountering any real friction at all, if they were sufficiently advanced,” Shuman says.
 “creates a new sort of challenge that very advanced bots can still get around, but introduces a lot less friction to the legitimate human.” CTO says.