These days, assume that any company you apply to will research you on line. They're allowed to use anything that's public information, which includes most social sites.
If you don't want employers to see something, it is your responsibility to keep it unpublished. Since companies may change their system's behavior and their privacy policies with little or notice, that means don't post anything you aren't willing to have exposed. And think twice before posting even in supposedly private services.
Basic principle: If you aren't paying for a service, you aren't the customer -- you're the product, and you're being sold to others.
Sorry, but that's the nature of the Net.