Let’s be sure everyone knows what constitutes plagiarism though, before we start deleting people’s works based on the claim.
It’s worth sharing a quote from US Copyright Law:
“(b) In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work.”
Copyright does not cover ideas and information themselves, only the form or manner in which they are expressed. For example, the copyright to a Mickey Mouse cartoon restricts others from making copies of the cartoon or creating derivative works based on Disney's particular anthropomorphic mouse, but doesn't prohibit the creation of other works about anthropomorphic mice in general, so long as they're different enough to not be judged copies of Disney's. In many jurisdictions, copyright law makes exceptions to these restrictions when the work is copied for the purpose of commentary or other related uses (See Fair Use, Fair Dealing). Meanwhile, other laws may impose additional restrictions that copyright does not — such as trademarks and patents.
So, just because some guy stole your idea to make an epic story about a necromancer who conquers the land with a band of undead giants, gets laid by his love interest, and has to fight a time warping monster, doesn’t mean he’s plagiarized anything or violated your copyright. It crosses the line, only when he uses your own words and descriptions, like using the same names and cutting and pasting your paragraphs wholesale right out of your story and into his.
This is also why we can have a Fan Section of stories about copyrighted characters and why you can parody just about anything you want – and even make money from it (ever watch mad TV? Or the Scary Movie lampoons?).
