I use a completely different name for my facebook profile and have a gmail account (unconnected) associated with it. I routinely get job offers for security work even though I have everything set to private.
I'm assuming that this is me showing up as linked to other people that are not so cautious.
I get on average about a message every 3 months from recruiters looking for 'fresh meat'. What I think they're doing is they're looking at friends on facebook, then their networks and making the assumption that the person will have a gmail account, then guessing what it might be. Sometimes I'm cc'd into variants of potential spelling like firstname.lastname@gmail, flastname@gmail etc. but most of the time it's a bcc. If you bear in mind that my profile has a distinctly odd name which used to be a googlewhack and that most of my friends friends on facebook are in the UK and in the same industry (I use multiple profiles for multiple purposes).
I'm assuming that this is me showing up as linked to other people that are not so cautious.