What is the silentCAPTCHA Complexity option?

silentCAPTCHA Complexity option is a part of the silentCAPTCHA AntiBot system.

It's accessible from within the main navigation menu > Security Zones > Bots & IPs > configuration:

Shield's improved NotBot system employs ALTCHA that challenges bots to perform complex work.

This complex work is compute intensive and inflicts a processing cost on bots. Bots typically won't do the work, and this option help to discriminate between bots and humans.

More complexity in the challenge is a bigger cost to bots, but may present a burden for legitimate visitors that use slower devices.

What Complexity to choose

Our CAPTCHA system uses the “proof of work” model. This means we present a complex, compute-intensive task to the visitor and ask them to solve it.

The challenge's complexity determines how difficult and time-consuming it will be to solve. Ideally, you want the challenge to be as tough as possible. However, legitimate visitors with slower or older devices may take longer to solve it. If you expect most of your visitors to be using mobile or older devices, choose a lower challenge complexity.

Adaptive complexity will try to present the most suitable challenge depending on the type of visitor.

If you select “adaptive,” Shield will adjust the challenge complexity based on how the visitor is presenting (typically using the user agent).

To learn more about the silentCAPTCHA, read the blog article here.