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. Unranked play will be unaffected by the change.
Valve says that "online services that provide phone numbers are not allowed," so potential workarounds to create a new "valid" number shouldn't work. In North America, data from the FCC-backed NANPA can help determine the source of any such online phone numbers, but it's unclear whether Valve will also be able to confirm international numbers in a similar way.