is there any smart way to defend yourself against sybil attacks? (apart from cookies,user agent strings,ip addresses)

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hello!
I am designing a website, and one of the features of the site is a forum. In this forum users get to vote up/down each others posts.
My big question is : how do I stop one user from creating multiple accounts and voting up his own post?
I cant ask for credit card info to certify users,when they create a login because that would deter a large section of the users. But is there any smart way to defend yourself against sybil attacks? (apart from cookies,user agent strings,ip addresses)

Any advice would be very much appreciated!
Thank you in advance!

Posted 23-Mar-11 23:29pm

noviceTaken

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#realJSOP · Answer 1 · 2011-03-23T23:41:00

Solution 1

You can probably mitigate it by not allowing people to register with free email domains, like hotmail or gmail.

You can also probably do some forensic evaluations to find accounts that login from the same ip address, and then disable all but the oldest of those accounts (assuming the oldest account is going to be the original one).

CodeProject experiences this kind of problem.

Posted 23-Mar-11 23:41pm

#realJSOP

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noviceTaken 24-Mar-11 7:04am

"probably mitigate it by not allowing people to register with free email domains, like hotmail or gmail."

charging a fee would greatly reduce the number of users and deter people from even registering right?