2015 was still just a baby when Gamereactor reported that Steam had beaten it's own record on concurrent users with 8.5 million people being logged in at once. Yesterday that number was smashed to pieces. No less than 9.5 million Steam users where online at the same time and the magical 10 million barrier should be beaten during the summer.
If you follow the most played lists on Steam, it should come as no surprise that Dota 2 was the most played game, followed by Counter-Strike: Global Offensive, Grand Theft Auto V, Team Fortress 2 and Football Manager 2015 - in that order.
Thanks Neogaf