I have two external Nest cameras (doorbell and plain external camera to cover front and back yards). I bought both of mine last year and know the two-factor suggestion is PLAINLY stated in the documentation and is suggested in the settings section of your web access configuration page.
Also, hacked passwords are traded online by hackers. If you're using a previously hacked password for your Nest account, you're at even greater risk of getting pwned. I know a password I used to use years ago is "out there", so I no longer use it. Point is, Nest didn't get "hacked" these stupid people got themselves hacked through their own ignorance and laziness.
Chris