Genesis said:WordFence. I use the free version for every one of my blogs. It's quite a heavy plugin, but I think worth having. What I also like about WordFence it has a blog and notifications pointing out all of the challenges one should look out for at the time they are happening - they are specialists in WordPress security for sure.
https://wordpress.org/plugins/wordfence/
I also load "Limit login attempts" for all of my blogs. I usually make the number higher just to make sure I don't get locked out myself. But it's good for many things too like whitelisting or blacklisting IP numbers. You can read more about it here:
https://wordpress.org/plugins/limit-login-attempts-reloaded/
Then there are common sense security for WordPress, like having all themes and plugins as well as WordPress script completely up to date all of the time. To ensure the passwords one uses are complicated ones, and to change them regularly. To regularly check up on the blog, particularly if one has comments turned on. To use spam software for controlling the comments, preferably have a system where comments have to be approved by the owner first. I have all of my comments turned off.