Hello,

Is there anyway to prevent a user from registering multiple usernames ?
If the answer is:
Cookie - Could be removed
IP - Could use a proxy or he could be on a dynamic IP

any other ways?

Make them give an email address and send a validation link to their email, this will stop alot of people, but still they could optionally create another email account at any of the free email providers. you could possibly also deny any free email hosts such as yahoo, hotmail etc. but alot of legit people use these accounts for everyday email and you would be denying them the ability to sign up.

maybe use a combination of several or all of these things. there really isnt a no fail way of doing this. people will find work arounds. the best you can do is make it as hard as possible.

hehe yes there is one good solution :) - paid accounts :) i doubt that some1 will still want to register another account :)

I had another way,
Make them enter some valuable information, such as Social Security no. etc for peoples in US and Credit card nos, or driving license no.
This will limit the fake or multiple accounts,
there are very few chances that users would register multiple times, with such crucial information.

Thank you PHPConcepts for your suggestion.

Nitin Gupta : They're actually international visitors :( plus, I don't think somebody would give out a credit card number on a normal registration :)

hmm...
but how can you limit the users to not to use free email accounts, coz most of the peoples are still using free email accounts. :P
so thats not a perfect way either.
you had to find some 3rd way out :D

well on my website i have something like this:
i store users ips+info about browser (updated each time they log in)
and i put cookie to theirs computers.
but i have 15 000 registered users and know that about 100 of them have more than 1 account
its web for uploading some sort of images so i track my website content + users activity and i can detect some abusive behavior sometimes
i tried little social enginering on them and deleted few accounts :) and wrote news explaining that i will not tollerate multiple accounts for 1 user and gave theme 24 hours time to delete it :) - guess what - 20% abusers deleted theirs second accounts :D and few even emailed me with "sorry" :)

obviously there is no other way that to store ip addesses + some extra info
and place cookies also

but as i noticed from time to time it is good to play social enginering :)

idea with blocking free email addresses isnt so good :)

Originally posted by Nitin Gupta
I had another way,
Make them enter some valuable information, such as Social Security no. etc for peoples in US and Credit card nos, or driving license no.
This will limit the fake or multiple accounts,
there are very few chances that users would register multiple times, with such crucial information.

That is a absolute horrible idea.
Your social security is not supposed to be given out...ever.
Making such info required will not only preven frauds, but prevent real people from joining too.

Originally posted by jasong
That is a absolute horrible idea.
Your social security is not supposed to be given out...ever.
Making such info required will not only preven frauds, but prevent real people from joining too.

lolz, it would surely prevent multiple accounts thoguh, however very few peoples would register there. .;)
Actually I am from India and didn't knew the importance of SSN, yesterday an american told me bout that
so i appologises for that
:D

Greetings!

Preventing duplicate registrations is really tasky. What I'll do probably is to encourage people to register only one account. You state it on your site that you allow only a single account to be registered. If they forget their password, provide means to retrieve it. Sometimes people use multiple accounts because they forget their login info! :)

Also, try to find out why they need to use multiple accounts in the first place. Is a single account not enough for them to use?
Post constant reminder about this. State it in your terms of service. Sometimes people tend to abuse if you do not explicity tell them that it is not allowed to use multiple accounts. So, make certain that the notice is prominent on your website.

A warning perhaps: If for any reason, the system detects multiple accounts of a single user, all accounts of the said user will be deleted without any notice.

I hope this helps. At any rate, you use all means possible.

:)