Windows 8/8.1 & Windows 10
All versions of Windows 8 and 10 have built-in virus detection called Microsoft Defender. As long as you keep your computer current on updates, then your device should be protected.
If you wish to learn about updating your personally-owned device, please view: Updating Windows & macOS on Personally-owned Equipment.
There are many antivirus products available for macOS systems. Some products are available for home use for free while other products require an annual subscription.