iThemes Security in one of many plugins from iThemes. It was previously known as Better WordPress Security. It is the most popular security plugin available. It has a free version and a Pro version. The Pro version is around $80.00 for a personal site. It’s included with any of the sites under my monthly maintenance plan.
“Most WordPress admins don’t even know they’re vulnerable, but iThemes Security works to fix common holes, stop automated attacks and strengthen user credentials. With one-click activation for most features, as well as advanced features for experienced users, iThemes Security can help protect any WordPress site.” It backups up your site on a regular basis, let’s you or your web master know if files have been changed and let’s you set unique ids for many of the default WordPress files. It also limits the number of times someone tries to log in with the wrong password. This stops or helps to prevent brute force attack. It protects your site from bots looking for 404 vulnerability and can even “lockout” bad users and bots.
It does warn that some of it’s setting may interfere with other plugins, but I have yet for that to be the case. With Pro, you get support as well as many additional features including 2- factor authentication.
I highly recommend the use of a security plugin and this is one of the best.