Why not install a live anti-virus program on him? He's not really going to be able to have any harm done to his computer if you manage to do that.
I live in a neighborhood full of blue-haired baby boomers. A foreign guy named "Steve" from "microsoft" calls them, convinces them to remote in and then shows them the warnings in the system log and says that those are viruses, which they are not. And charges them $400 for the lifetime support scam.
Simply installing a virus scanner will not fix social engineering.
https://www.youtube.com/watch?v=WrdrwiTlVooThis is what happened.
He did what I hoped he woud do. He quit the Net. I was glad so I wouldn't have to worry more about socail engeneering.