If you have a low-end PC and can't handle the virus situation, the best answer is Linux...which in turn is a "cousin" to the MacOS except Linux is free and runs on standard PC hardware (including old cheap stuff). Linux and MacOS (starting with version 10) are both "Unix family tree" operating systems scaled down from university mainframe setups. The Unix world solved computer security issues in the late 1970s that Windows is still grappling with. Windows is a scaled-up toy for PCs; Linux is a scaled-down-for-the-PC monster also used in the world's fastest supercomputers.
There's a problem though: setting up Linux for the first time means being a bit "geeky" unless you have somebody available who already knows it. I've guided a bunch of people into transitioning to Linux (generally the Ubuntu flavor) and it works great so long as I convert their data over and do the initial setup.
After that a total PC newbie can run it just fine. With zero anti-virus software, because it's immune to all that Windows malware.
If they have the horsepower for it (Pentium4 CPU with 1gig RAM minimum) I set them up with a Windows XP "virtual machine" that runs underneath Linux whenever they want - that way any specifically Windows thing they need still works. Linux ends up acting as a "super firewall from hell" for Windows, you can jump instantly from Linux to Windows, and you do all your web-stuff and EMail in Linux where you're protected.
But it's that first step that can hose people.
I jumped to Linux almost two years ago when my XP laptop caught a bad bug despite all possible updates and a paid-up copy of ZoneAlarm Pro anti-virus and software firewall. Something tried to zombify me regardless; after a three-day bughunt I downloaded Ubuntu and have never booted Windows as my primary OS since. The learning curve was doable on my own but, I'm a geek
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