A recent challenge has been posted on the main site. A user discovered that it was copied word-to-word from an external source, and that challenge has been closed as off-topic, with this reason: "Questions without an objective primary winning criterion are off-topic, as they make it impossible to indisputably decide which entry should win". That does not seem right to me, because it had a winning criterion. So, the question is: What close-reason should we choose for challenges that are copied from external sources?
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If a question is a clear violation of copyright then you should raise a custom flag to notify the moderators, providing a clear explanation of the situation with links to the source where possible. That's a backstop which ensures that the situation will be addressed. Additionally:
- Comment to explain the problem. This may occasionally result in the OP editing the question to credit the original source and show that it is under a licence compatible with CC BY-SA 3.0. It may also result in the OP deleting the post. And it should deter people from answering, which is in everyone's best interests if the question is heading for the bit bucket.
- High-rep users can vote to delete a question subject to various conditions. This is the only part of this answer which I think could be controversial: since we're given extra powers in order to reduce the load on the mods, I think it is appropriate to vote to delete once OP has been given a chance to edit as mentioned in the previous point. And since we can only vote to delete once the question is on -3 (or has been closed for 48 hours), I think it is also appropriate to downvote the question in order to enable high-rep mods to delete it.