I sometimes Google my name to see the personal information that strangers can easily get about me.
Recently, I was very surprised to notice that my full private Linkedin profile was available on some web site called Yatedo.
Yatedo calls themselves a People Search Engine.
What they state to be doing is getting all publicly available information about an individual and put it on their web site.
Now I've never made my Linkedin profile or picture publicly available, you need to be my contact to see that.
When you go on their website, you can "reclaim" your data. Before you do that, they will require that you enter you Linkedin (or Facebook or the source of the data) credentials...
I guess you now understand how they get access to personal data that is supposed to be available to your contacts only.
I have not yet found a simple way to delete my data on Yatedo.
It's a french site by the way, and there is some organism that has the authority to get your data removed. But before filling a claim with them, you need to send a written request to Yatedo to remove your data and wait 2 months...
They've also somehow gained access to my Facebook profile picture while it's available only to my contacts, and my profile setting are quite private (I don't even show up in Google).
So beware. It only takes one of your contacts getting lured into Yatedo, and then they gain access to your data.