Windows Defender is all the On Air PC needs, as long as users are responsible & aware of online threats.
Do not use the internet on the On Air PC. Do not open emails from unknown sources. Do not click on random links. Follow those rules & the On Air PC will be less likely to be infected.
When choosing a backup solution, there are many factors to consider: the amount of data, backup method, backup speed, & the necessary amount of computer expertise.
You could spend a one to two hundred dollars on a 2 terabyte drive. Do you really need that much space? Probably not. 750GB to 1 TB is more than enough to accommodate the growth of multiple audio libraries.
Online storage services or Cloud based programs seem great until you realize how incredibly slow they are & how much of the PC's processing is used to backup online. During a scheduled back up, the online storage software will pull memory & processing away from the automation system, causing the PC to slow considerably & possibly glitch audio.
Backing up across the network, on a wired connection, to a server is a good alternative.
An external USB hard drive as a dedicated automation backup is the best alternative.
Once you've a full backup of your automation folder, we recommend a manual backup of the specific automation folders containing the schedule & setting information to an external hard drive on a weekly basis. Once the back up is finished, properly eject the external USB drive & store it a safe location. Choose a day & time; make it a habit & when your PC's hard drive fails, which it will, you will not be left in a lurch.
We, also, recommend keeping an up-to-date back up of new audio files on the production PC. When you save a new file to the automation's import folder, save a second instance on the production PC in an archive folder.
As with anything computer related, if you prepare for the worst, when the worst happens, you'll be able to quickly get back on the air using the regular backup.