If you own and operate a Wordpress website on your own servers you need to of course keep it updated as there are many updates each year as they are constantly updating core of the site to help prevent attacks as well as keeping it new and fresh as the internet websites evolve.
As a website owner or webmaster taking care of your clients websites you need to do a couple of things that will help stop hackers cold in their tracks. Plugins are a simple way but not best solution for everyone but they certainly helped me. I had one website being attacked everyday, weekly and if I did not back it up it would be a total loss as you can't rely on the hosting provider to have your backups and if they did most would be dated beyond the site current content.
Struggling with this for months I have tried many thing and a few weeks ago I added one plugin, upgraded it and walla - instant stop as when I upgraded the plugin I was able to block all countries except USA and that stopped them mean hackers cold. Then to my surprise I get an email that someone logged in as the 1st plugin called Wordfence sends you emails on all kinds of things as you select to be notified as I do.
Wordfence is really good and there's a nice cache system that speeds up the site by 30 - 50 times and that's not percentages. Best of all it's FREE but if you upgrade it adds many other features but the one I love the most is it will send you an SMS to your phone providing you with a code to enter with your password.
The other plugin I added yesterday and I added it cause I kept getting notices of the hackers trying to log-in and I thought there must be a cool little plugin that hides the wp-admin and of course I tried a few but found the Lockdown WP Admin to be simple and quick. The notices stopped as they can't find the login page now.
These two are the only plugins I use for the WP sites now except if the wordpress website theme has additional plugins such as contact form etc.. most importantly is to keep your plugins updated. Wordfence will send you a notice each time a plugin or just about anything needs updated or out of sync to help prevent hacks.
Good luck with your websites and if you've ever been stressed by a hacker.. these two plugins should bring peace of mind.