There isn't a definitive "best" or flawless security plugin available; however, we have yet to come across one - no tool can guarantee complete online protection. BUT, by adhering to security guidelines, employing a high-security hosting service, and utilizing well-established security tools (which is exactly what we do), you can minimize the risk to the utmost and significantly decrease the chances of your... Source: 12 months ago

First, run a site backup -- both the database and static files on the server (e.g., theme files, image uploads). Ideally you'll also know or figure out how to restore the site with said backup. The plugin UpdraftPlus has a free tier you might start with. I use it on a personal site to run daily backups automatically, and have used it on employer websites in the past. You should be running daily backups if you... Source: 12 months ago