On Quant SE, a user has been blindly upvoting some of the top users. Specifically, he has been maxing-out his daily vote limit by upvoting every answer from a small pool of users. I warned this user last week, but that didn't seem to stop the "vote stuffing".
I think this is a problem because the fraud detector could cancel the votes, which means that the reputations will swing wildly. Is there a protocol for handling a user like this?