[bruce511]

Windows out the box is pretty secure. Make sure they are behind a NAT router and sll incoming connections are blocked.

AV is built in and works well.

Of course it's not Windows you should be worried about. It's about programs that they download and run, or come via email. That's best solved with education, and frankly applies to phones as well as desktop.

A healthy amount of fear when it comes to new software, or opening docs is no bad thing.

And please don't foister things like Libre Office on them. They are a poor solution to those used to Office. It sounds like you've tried that before :)

Only techies care about mundane things like license and freedoms etc. Regular people just want working software, that they are used to, which just works. These days that means Windows or Mac, or whatever they had before.