Dota 2 will require players to link a phone number to their accounts to participate in ranked matches, to curb the creation of multiple accounts by a single user.
The abusive practice, called “smurfing,” is done for many reasons. It’s frequently done by veteran players posing as beginners, or by those getting around being placed in the game’s low-priority matchmaking queue for bad behavior. Whatever the case, multiple accounts "create a negative matchmaking experience at all skill brackets," Valve said in a blog post announcing the change. It takes effect May 4.
Valve acknowledged that a linked phone number will not eliminate multiple accounts for a single user entirely. "Our goal is to add just enough friction to this process that the number of players doing this will be noticeably reduced," Valve wrote.
Unranked play has no such requirement to link a phone. However, "Having more players using their primary accounts will have a positive effect on both Ranked and Unranked Matchmaking," Valve says.
Dota 2 accounts that already have phone numbers linked will still need an extra confirmation step before playing ranked matches after May 4. Phone numbers may be changed but that number will be ineligible for use for three months before it can be registered on a new account. And yes, phone numbers provided by online services, such as Google Talk, won't be allowed.
There are other changes introduced with this patch too. In matchmaking, if a player's solo matchmaking rating is higher than their party rating, they will get a higher matchmaking rating — splitting the difference between the solo and party values. "We've found that when a solo MMR is dramatically higher than a party MMR, the match becomes extremely volatile," Valve explained, "resulting in an unpleasant and uncompetitive experience for both teams."
Also solo queueing has been restored, meaning that players may choose to be matched only with other solo players in ranked matches. Some other penalties and countermeasures have been introduced to curb toxic behavior in games, and South Africa, India and Dubai have been removed as ranked matchmaking regions. Their low populations had made them targets for ranked matchmaking abuses by players from outside the regions. Players in those countries may still play ranked matches in nearby regions.