Correct me if I am wrong, but by looking at the way the message is created, I think, LinkedIn is acting a kind of spammer these days. Shall we lodge protest against it as a community?
What happens is that anyone who joins is pushed to run their contact list through them "to look for connections", then LinkedIn sends an invitation to any address not already noted as a member. So it's spammy but in an especially slimy user-initiated way.