Social network invitations

As if I was not irritated enough about social networks, they have now also become the source, directly or indirectly, of a big percentage of the spam we see. Invitations, always from people I don't know, from Facebook, LinkedIn, and many sites I haven't heard of, coming in, in a steady stream. It's like these parasites (para sites) simply won't stop until they have infected every living organism on earth.