Proof of Work

Proof of Work (PoW) is an invisible challenge where the browser solves a computational puzzle.

How It Works

When a PoW challenge fires, the browser computes hashes in the background until it finds one with enough leading zero bits. Depending on the tier that is 18 to 22 bits, i.e. roughly 0.26 to 4.2 million attempts — half a second to a few seconds on a typical device. If the machine cannot manage it in time, the visible arithmetic captcha follows.

Why It Works Against Bots

Every request costs CPU time. A human submitting one form barely notices the delay. A bot trying to submit thousands of forms is significantly slowed down because each submission requires real computation.

Fallback

If the browser cannot complete the PoW challenge (e.g., very old browser or JavaScript disabled), the Math CAPTCHA is shown as a fallback.