What is to stop circles of friends and cliques from synchronizing their upvoting and downvoting activities? Does Stack Overflow analyze the voting data to look for collusion and conspiracy patterns?

I am asking out of curiosity, not because I want to use this information. Sometimes a little security by obscurity can be a good thing.


Yes, the system analyzes voting data and will effectively cancel votes it considers to be fraudulent.

See the "Vote Fraud and You" blog post for more details.

Note that getting a set of people to vote for each other is only one possible form of vote rigging. I suspect that more often than not, it's asymmetric with the target knowing nothing about it.

A few times I've reported "odd" voting where suddenly (in a quiet period) I've had 10 different answers (including old ones) receive a single upvote almost simultaneously. Usually after reporting this to the mods they've found that it's a single person who's decided to visit loads of my old posts and upvote them. This is effectively a form of bias, and the votes are cancelled.

The exact rules followed by the automated system have not been revealed, for obvious reasons. (Indeed, if SO is ever open sourced, it'll be interesting to see whether this means there's suddenly a lot more fraud which is done in a way designed to squeak by the system. I'd hope not, but you never know...

  • Thanks. I am new here but I was unaware that downvotes gave the downvoter -1 rep. But might this also stop someone from downvoting a post which should probably be downvoted? Jul 25 '09 at 19:42
  • I don't see that open sourcing SO would necessarily expose the rules. It may expose what rules were possible, but the specific triggers and weights used to make decisions may well be data fed into the system rather than code copiled into it.
    – Mark Booth
    Mar 24 '10 at 16:56
  • But could the system detect a group of friends that occasionally cast small number of votes for each other and a many votes for a random selection of other questions with each cast vote separated by a random period of time?
    – Zoredache
    Mar 24 '10 at 17:53

Jeff runs some sql jobs that check for vote fraud

  • That is good, but a complex vote exchange network with enough users that it would not be obvious could randomize who votes who. People are doing this on sites like Digg and Reddit as we speak. Jul 25 '09 at 19:39

200 rep-cap is there partly for this reason.

  • Yes, I thought that was a good idea to put a hard ceiling on how much rep a user can accumulate. I'm working on an online MUD game and I have a similar strategy with "stamina" on how many moves a player can do per day. Jul 25 '09 at 19:37

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