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Glossary · Security

CAPTCHA

Completely Automated Public Turing Test to Tell Computers and Humans Apart

In plain language

A small test on a web form that tries to tell real people from automated programs.

The metaphor

Like a bouncer asking a quick question only a person can answer.

Going deeper

How it works

  • It asks you to pick pictures or tick a box.
  • It slows down bots that guess passwords or flood forms.
  • Some work silently in the background.
  • Attackers have ways around them, so they are one layer.
In practice
  • A contact form uses one to cut spam.
  • A login page adds one after failed tries.
  • A booking form checks behaviour in the background.

A question owners ask

Is it worth adding to my contact form?

Yes, a simple one cuts a lot of junk submissions.

Related terms
AAAAuthentication, Authorization, and AccountingAccount takeoverACLAccess Control ListAdmin accountAESAdvanced Encryption StandardAES-256Advanced Encryption Standards 256-bitAISAutomated Indicator SharingAPTAdvanced Persistent Threat

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