How can you stop people voting more than once?

The system matches each completely anonymous vote against an IP address and one or two other details to prevent this from happening.

It's not 100% proof against fraudulent voting - almost no system can be - but greater levels of protection would require much more money than we have, and would also mean collecting more personal information from our voters, and for now this is something we would prefer to avoid. These early Global Votes are therefore something of a Beta-Test, but it is our intention to make the system more and more robust over time.