The gaming firm Valve has halted trading of some in-game items in its popular multiplayer shooter Counter-Strike: Global Offensive after discovering that “nearly all” of the trading was part of a money-laundering scheme run by “worldwide fraud networks”.

In CS:GO, players can earn containers with cosmetic items, which can be unlocked using keys bought either in-game or for real money from other players.

Valve said it had closed the market between players, and in patch notes for the latest version of CS:GO – first reported by Motherboard – it gave its reasons.

“In the past, most key trades we observed were between legitimate customers. However, worldwide fraud networks have recently shifted to using CS:GO keys to liquidate their gains,” it said. “At this point, nearly all key purchases that end up being traded or sold on the marketplace are believed to be fraud-sourced. As a result we have decided that newly purchased keys will not be tradeable or marketable.”

Valve did not go into detail, but it is likely the trading was used to launder income from credit card fraud and other financial crimes. Buying and reselling digital goods is a popular way for financial criminals to cash out from identity theft. In the past, iTunes and Amazon gift cards have also been popular.

Counter-Strike has previously faced criticism from regulators for enabling gambling by children. In July the Gambling Commission’s programme director, Brad Enright, told MPs that CS:GO was responsible for more enquiries than any other game.

“We’ve had dialogue with Valve Corporation,” Enright said. “Where we draw their attention to particular games where British consumers including children are gambling on those sites, they have closed them down.

“We’ve said that’s not a sustainable approach. They’ve created this situation … and there’s an onus and responsibility on them to address the byproduct of how they’re operating.”