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Similar to bots posting spam posts and blogs is it possible that bots with legible registered accounts go around the site flagging or downvoting everything on the site. If yes, what can I do to prevent this? For example, I understand there are numerous ways to try and prevent machine generate activities like CAPTCHAs, honeypots or third-party spam detection services and so on, but what should I use here?

Also are there anymore threats in implementing flagging/downvoting?

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    Consider this site. It uses reputation gained by positive participation as a barrier to down-voting and at a cost in reputation on less - see stackoverflow.com/help/privileges/vote-down – zedman9991 Dec 4 '13 at 13:31
  • @zedman9991 i am actually not dealing with reputations...i just wanted something like say 10 flaggings/downvotes cause the post to be deleted. how should i implement my policy here...Thanks! – DevD Dec 5 '13 at 8:29
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The easiest way to prevent it is to have have a reputation or karma system like you see on most sites, this one included. If you can't implement such a system, then you're not left with much in the way of prevention aside from the usual bot prevention methods you've mentioned. What you would need to focus on would be detection.

A detection algorithm would help you identify and block any bots that make it through your CAPTCHAs, etc. This algorithm would look at a number of user metrics and compare them to some baseline average, any user with a one or more anomalous metrics would get flagged for investigation.

Some metrics could be:

  • age of account vs number of up/down votes
  • recent rate of up/down votes
  • ratio of up:down votes.
  • ratio of votes to page/article views
  • ratio of votes to comments
  • ratio of votes that match the majority opinion

The list would obviously depend on the site and interactions available, but you get the idea.

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