CAPTCHA

internet security · clever passwords · human vs robot

Stops spam bots. CAPTCHAs protect websites from spam and attacks by forcing visitors to prove they're real people, not computer programs trying to mess things up.

Twisted letters test. The most common CAPTCHA asks you to read blurry, distorted letters and numbers, which humans can figure out but robots usually can't.

Named after Alan Turing. CAPTCHA stands for 'Completely Automated Public Turing test to tell Computers and Humans Apart,' named after a famous computer scientist who thought about what makes humans different from machines.

Many types exist. Modern CAPTCHAs include clicking traffic lights, selecting matching images, or solving simple math problems instead of just reading warped text.

Quick but secure. A good CAPTCHA should be impossible for bots to beat but take humans less than 30 seconds to solve.