These are the main mechanisms we offer to block repeat voting:

1) Blocking repeat voting using the browser - this method is not very strong, as users can delete the browser "memory" to circumvent this mechanism.

2) Blocking repeat voting using IP addresses - this method is much stronger and more than enough for most of the cases, however, a more sophisticated hacker can overcome this by writing a bot that switches IP's automatically - not trivial, but possible.
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In addition, from the results dashboard, you can export all the vote submissions to verify there aren't any cheat patterns (e.g. irregular submission times, bursts of votes to a specific side, etc.).

1) Edit your poll

2) In the Block repeat voting drop-down, select Block based on browser & IP

In high-profile voting scenarios where voters are motivated to cheat, we recommend not showing users the results before the voting ends. When users see the results, they are more prone to try to "hack" the poll.