Sony Online Entertainment's DC Universe Online has received 120,000 new registrations since it went free-to-play earlier this week.
The superhero MMO was first launched for with a subscription model back in January, but dropped these fees on Monday.
The surge in new users for the PC version was confirmed by SOE boss John Smedley, who reported on Twitter that the game's overall userbase has risen by 400 per cent.
He also confirmed that a new TV and online marketing campaign will kick off this month to help raise awareness of the transition to free-to-play.
DC Universe Online is also available for free on PS3.