Enlarge / Everyone in this picture better have a valid phone number... Dota 2 maker Valve is taking serious action to cut down on the prevalence of smurfing—using a secondary account in order to to play against opponents of a lower skill level. Starting next month, Dota 2 players will need to have a unique, valid phone number associated with their account to take part in the game's ranked matchmaking pool. Ideally, the move would ensure that a single person can only have a single Dota 2 account, so highly skilled players couldn't pretend to be novices in a ranked match.