Jetpack’s Brute Force Attack Protection prevents malicious login attempts and protects your site.
The Jetpack Protect feature will help protect your site from “brute force” attacks that might be trying to slow or shut your site down. It can also help with unwanted login attempts to your admin area.
To enable this feature, go to: Jetpack Settings > Security and enable Protect. If you ever find yourself or another person prevented from accessing the admin area you can add their IP address in the Whitelist area to prevent it from being blocked from logging in to the site.
If you’re looking for a little extra layer of security on your site you might want to check out the Jetpack Protect feature.