The feature is indeed automatically enabled when you update from Jetpack 3.3.2 to Jetpack 3.4+, unless you already use one of the following plugins:
- Limit Login Attempts
- Captcha
- Brute Force Login Protection
- Login Security Solution
- WPSecureOps Brute Force Protect
- BulletProof Security
- SiteGuard WP Plugin
- Security-protection
- Login Security
- Botnet Attack Blocker
- Wordfence Security
- All In One WP Security & Firewall
- iThemes Security
If you think we forgot a plugin on that list, let me know!
If you’d like Jetpack to stop automatically enabling some of the new modules, you can add the following code to your theme’s functions.php or to a functionality plugin:
add_filter( 'jetpack_get_default_modules', '__return_empty_array' );