Google Chrome malware infections follow you on both PC and Mac?

As the go to technology person for a lot of my friends and family, I've noticed an interesting development. Quite a few of them have been getting malware infections in Chrome!

They'll somehow install a Chrome extension unwittingly and then through the magic of Chrome's invisible sign-in process once you sign into gmail or youtube, they'll infect whatever other computers they use. Other browsers that they have installed like IE or Safari stay uninfected.

Have you guys noticed this? It seems to be a pretty big issue.