what is blind reference check

have you ever tried to search your own email address or phone number in Google?
what does Google turn out?
are all these results good for you?

what if you provide your this email and/or phone number to your currrent/potential employer?
I do know some companies not only contact the references you provided but they also check your contacts online. how do they do it? just Google "blind reference check".

how do they find your contacts?
think about Linkedin, Facebook, Twitter, any online forums...

if they did not get any response or any positive response, it's bad sign for you.