Google engineers are working on an improved version of the reCAPTCHA system that uses a computer algorithm to distinguish between automated bots and real humans, and requires no user interaction at all.

Called "Invisible reCAPTCHA," and spotted by Windows IT Pro, the service is still under development, but the service is open for sign-ups, and any webmaster can help Google test its upcoming technology.

Invisible reCAPTCHA comes two years after Google has revolutionized CAPTCHA technologies by releasing the No CAPTCHA reCAPTCHA service that requires users to click on one checkbox instead of solving complex visual puzzles made up of words and numbers.

The service helped reduce the time needed to fill in forms, and maintained the same high-level of spam detection we've become accustomed from the reCAPTCHA service.

The No CAPTCHA reCAPTCHA service was last winter at the heart of a controversy when the Tor team accused CloudFlare of forcing its users to verify themselves through reCAPTCHA visual puzzles when accessing sites protected by CloudFlare.

The introduction of the new Invisible reCAPTCHA technology is unlikely to make the situation better for Tor users since CloudFlare will likely force them to solve the same puzzle if they come from IPs seen in the past performing suspicious actions. Nevertheless, CloudFlare started working on an alternative.

In the spring of 2016, a trio of researchers devised an automated attack that could crack Google's reCAPTCHA system, with a high degree of accuracy.