multi signup

I'm playing a browser game and wanted to create multiaccount, the game has an easy sign up and do not need anything else to join but when I try to register a 2nd time it asks me to verify the account trought cellphone.

What the server could be checking? ip, mac address? what else can be and how I do it..

Maybe it's a little bit more helpful if we know the name of that game.

nothing to do with gamehacking.

#closed