Which security modules do you have ?

Our free plan includes ‘Protect’ which is designed to protect your site against brute force attacks, you can also force Two-Step-Authentication for your site via our Secure Sign On module. If you move to our Personal plan, you will also get Spam protection, moving further up to our Premium and Business plans will get you malware scanning.

You can read more about Protect and Single Sign On here:

https://jetpack.com/support/security-features/
https://jetpack.com/support/sso/