[serg_chernata]

There are already good solutions below. The one thing I would add is that this may not be a "silver bullet" kind of problem. I'd throw everything I can into the mix to create layers of protection. Educate them but also add software solutions to the mix.

A small addition, how often do they need to install new software after initial setup? Maybe take away admin privileges?

[throwawaywxc]

Should hardly ever need to - but I am rarely at home so would prefer not to be in a position where any time they need to do something I need to be present.

The only real software he would need at the moment is for photoediting