From the Dota 2 website:
Today, we permanently banned 90,000 smurf accounts that have been active over the last few months. Smurf accounts are alternate accounts used by players to avoid playing at the correct MMR, to abandon games, to cheat, to grief, or to otherwise be toxic without consequence.
Additionally, we have traced every single one of these smurf accounts back to its main account. Going forward, a main account found associated with a smurf account could result in a wide range of punishments, from temporary adjustments to behavior scores to permanent account bans.
On top of my head (uneducated guess) :
- multiple accounts regularly logging in through a single IP
- day/time login patterns
- same champion pools
- consistently stomps games
- frequent higher than average KDA
- frequent higher than average CS/min
- higher than rank level winrate
- higher than rank level MMR
These items taken individually don’t tell much. But when cross-referenced with other data, I’m pretty sure it becomes clear really fast when someone is smurfing.