Mechanisms for blocking repeat voting
These are the main mechanisms we offer to block repeat voting:
1) Blocking repeat voting using the browser - this is not very strong, as users can just delete the browser "memory" to circumvent this mechanism.
2) Blocking repeat voting using IP addresses - this 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 easy, but possible.
In addition, from the report 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).
To add IP vote blocking
1) Edit your poll
2) In the Block repeat voting drop-down, select Block based on browser & IP
Other recommendations
In high-profile voting scenarios where voters have the motivation to cheat, we recommend not showing users the results before the voting ends. When users see the results, they are more prone to try and "hack" the poll.