Despite the difficulty of these tests, bots could still defeat them using machine learning while humans struggled, meaning CAPTCHA often decreased user experience while failing to prevent bots from entering a website. Early CAPTCHAs involved identifying obscured images of letters and numbers, but these images, while difficult for bots to bypass, were often hard or impossible for humans to decipher as well. The solution to this was a variation of a Turing Test called CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart), a challenge-response test used to determine if a user is human.
When the internet was first gaining massive popularity in the early 2000s, it was flooded with bots.
