Good stuff has been said, but my perspective is to treat them like lying children, instead of taking pro-active action against them. Just let everyone know about them, post responses which indicate plagiarism, and recommend people don't answer them and downvote them.

I mean, why get so upset over it? Do you want to get an ulcer by constantly watching their posts then digging for the plagiarized source?

I propose actively ignoring them, and hope they go away. If they know they can agitate us, they will. And that could get ugly if they sign up for a bunch of phony accounts and just start plastering the nodes with junk..... then the janitors will be forced to take very undemocratic action, like summarily deleting nodes.