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Application & OT Security · Foundational

CAPTCHA

A challenge-response test intended to distinguish humans from automated bots.

Definition

CAPTCHAs slow automated account creation, credential stuffing and scraping, but solving services and AI can defeat many of them and they reduce accessibility. Modern alternatives include invisible risk-scoring challenges and proof-of-work, combined with rate limiting.

Example

A login form shows a CAPTCHA after three failed attempts from the same IP.

Exam tip

CAPTCHA is anti-automation, not authentication; use it with rate limiting.

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