Proton, the company behind the end-to-end encrypted Proton Mail, released PRoton CAPTCHA, a layered system to differentiate between humans and bots. For the past decade and a half, CAPTCHAs and reCAPTCHAs have served as resource gatekeepers to deter bots from creating fake accounts, spamming forms, and executing brute-force attacks to guess usernames and passwords.

Source: Dark Reading: Cloud