I think anyone who is young enough to have been a child during the advent of internet communities has heard that sort of shit from their parents in some form or another.
Back in the days when the internet was new and scary.
And really, it wasn't just the early advent of internet communities. It was the common line of thought right up until grandparents started joining facebook. Now everything has went to the other extreme and it is considered anti-social to not put all your information out there through social media.