Garry's Mod, the digital world construction kit which uses Half-Life 2 physics and assets, is said to have generated "about $22 million" for its creators Facepunch Studios.
But according to software creator Garry Newman, the bankable figure is "less than half" of the revenue.
"Over 7 years, GMod has made about 22 million dollars," Newman said on his personal blog.
"We get less than half of that though. Then the tax man gets a bunch of that. Then when we take money out of the company the tax man gets a bunch of that too."
Newman also confirmed the group is working on a new PC game, as well as adapting Garry's Mod for the Linux OS.
"Hopefully we're gonna get the Linux version out. Then hopefully we'll move to SteamPipe, and I'll get the NextBot stuff hooked up. then I want to do another Gamemode Contest," he said.
"But I want to knock out a bunch of game mode creating tutorials first to help people get their foot in the door."