PC games firm Valve has revealed that it is trading or resale of container keys for its online shooter Counter-Strike: Global Offensive (CS:GO) over concerns they were being uses for money-laundering purposes.

In a blog post on the game's website, the developer said that the keys that unlock the title's equivalent of loot boxes - and are purchased with real money - were being used to launder money. This is a change from the past when Valve says that key trades were mostly "legitimate customers."

"However, worldwide fraud networks have recently shifted to using CS:GO keys to liquidate their gains," the company wrote.

"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.

"For the vast majority of CS:GO users who buy keys to open containers, nothing changes; keys can still be purchased to open containers in their inventory. They simply can no longer be traded or transacted on the Steam Community Market.

"Unfortunately this change will impact some legitimate users, but combating fraud is something we continue to prioritise across Steam and our products."

In the past, Valve's shooter came under fire for skin gambling with one site - CS:GO Lotto - in the spotlight after it was found that two prominent YouTubers were heavily promoting the site and not clarifying that they indeed ran it. This ultimately led to new influencer transparency guidelines from America's Federal Trade Commission.

Meanwhile, French players can now see the contents of a loot box before spending their hard-earned cash. This follows the business model coming under fire around the world in the wake of 2017's Star Wars Battlefront II controversy, with countries taking measures that restrict the mechanic. Belgium, for example, straight-up banned loot boxes.