what are the best method to prevent multiple accounts...?

Answer 1

For ip filtering you can use services like maxmind. They filter bad and fraudulent traffic, vpn, proxkes, anonymizera and similar.

Answer 2

You could use the IP. But even that can be masked/changed.

Answer 3

in school use id
in real world use phone number or valid home address. maybe

Answer 4

let ask google about that since that is the method used by google to verify gmail account.

Answer 5

If you're serious about that use something like big guys - youtube, facebook, gmail use: ip + browser agent + screen resolution + cookies + email verification with junkmail (temporary mail) exclusion. Possibly add phone check. I remember youtube used even flash cookies and vpn and proxy detection.

Answer 6

There are code snippets for things like user agent checking, screen resolution, mail... Nust go google for them. For junkmail you must use some database, or create your own, of sites like mailinator and similar junkmail sites so you can decline mails with that domains. For vpn and proxy it's somewhat tough. I'm not sure about that, but i think you need to rely on some online database of their network ip adresses.

Answer 7

Search for code snippets on net - "Google is your best friend..."
And maxmind have their own api, I used them for geolocation years ago

Answer 8

control by email signup

Answer 9

I mean the system would send an email to user whenever they sign up with their email. They then have to confirm the sign up by clicking a confirmation link from the email.

Answer 10

good idea but if the user use vpn or proxy what will you do ?

Answer 11

good idea but How do I learn these skills?

Answer 12

do you know where I learn these

Answer 13

good idea but e-mail easy to rigging

Answer 14

use email confirmation

Answer 15

Easy email fraud lot of sites gives you temporary email

Answer 16

good idea but how to send sms in php to confirmation phone

Answer 17

I know but easy to piracy