Ask HN: Clans in news recommendation site?

I was wondering what will happen if a "Clan" forms on News.YC or reddit etc. By a clan, I mean a group of users who always upmod each others articles or comments etc and possibly downmod certain topics? Even if there are only 7-8 user clans, the stories submitted by a clan can rise very fast to the top. How will you detect and deal with them? I dont believe any clans currently exist and its just a hypothetical situation.