CAPTCHA
A test that tries to tell whether an action is being performed by a human or by automated software; it protects forms and login pages against bot attacks.
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Why it matters
Bot protection reduces form spam, fake sign-ups and mass login attempts with stolen passwords. But hard puzzles tire real users and can create barriers for people with visual impairments. Many solutions today work invisibly using behavioural signals, and they are more effective when combined with rate limiting.
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Example
A site's contact form receives hundreds of spam messages a day. Once invisible bot protection and rate limiting are added, the spam almost stops, and real visitors never have to solve a puzzle.
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Common mistake
Using only a visual puzzle without offering an audio or otherwise accessible alternative. Some users can never submit the form.
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Related terms
Related services and guides
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