Would he generally install software if he sees an ad for it, or was that special because it wasn't obvious that it was an ad and therefore had more trust (like some security product company saying "your door is unsafe, buy our product" vs your friend telling you that your door is unsafe)?
It's strange that Chrome doesn't take the bookmark, bookmark-bar status and new-tab-page from firefox - if they did, he likely wouldn't have noticed and called you.
I'd wager it was the "Browse Faster" ad - which coming from Google is a tempting click.
Just a small aside on the grandparents topic: my grandfather lost every dime to email scams in the late 90s. The man was a Westpoint grad who served in the Pacific theater as an officer, and in his last years he clicked away his retirement. Installing Chrome is a pretty benign mistake but boy, we need guard rails for our older folks.
I most definitely agree regarding older folks. Unless you have a very good feel for the digital environment, consider everything harmful, and all emails you don't expect, know the sender for (or where the sender behaves atypically) to be malicious. It's a touch lesson to teach, much like stranger danger for kids, and it's going to become more and more important the more stuff moves online. When you're required to file your taxes via a website, you're much easier to attack than when you took a bunch of forms, completed them and then mailed them to the government (or, if you're late, go and put them in their mailbox). Plus the general inconvenience of good security ("why can't I use the same password?"), fun times lie ahead.
>Would he generally install software if he sees an ad for it, or was that special because it wasn't obvious that it was an ad and therefore had more trust
That's the trick in here. He doesn't install anything else off the internet. It only happened with chrome. And I am positively sure it was due to the very sneaky and underhanded chrome ad on the front page of google itself (a place where it is impossible for anyone else to get a single ad).
It's strange that Chrome doesn't take the bookmark, bookmark-bar status and new-tab-page from firefox - if they did, he likely wouldn't have noticed and called you.