title: How to prevent the most number of cheaters for polls?
body: <p>On my website we run a contest system and users vote for other user's content. We recently caught someone creating multiple accounts to vote multiple times (consecutive id numbers, and votes within a couple minutes). We would like to prevent that from happening again. Judging how Times handled their "Most Influential Person of the Century" poll, even the big guys get it wrong.</p>
  
  <p>Currently we log User ID's, vote date, and IPv4 addresses (via $_SERVER['REMOTE_ADDR']).</p>
  
  <p>What things can I do to prevent or make it more difficult for someone to vote fraudulently?</p>