proof of work

• Javascript Hashcash Proof of Work Dec 04 2017
  Suppose that you developed an app that will give users free stuff when they click a button. Obviously, there’s nothing stopping one user from spamming the button one million times and collecting a whole bunch of free stuff. If you wanted to prevent that, you could use something like a CAPTCHA, or perhaps give each user a session and cool off period. You could also implement something called a proof of work system.

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