Players of the hugely popular Fortnite video game are being urged to be vigilant as malicious hackers kick off campaigns to hijack accounts.
In recent weeks, many Fortnite players have reported via social media that their accounts have been taken over.
Many have been hit with high charges for games and other items they never bought.
Fortnite maker Epic said it was aware of the attacks and was looking into them.
The game is a co-operative survival shooting title that lets players build structures out of materials they scavenge from the game world.
Its most popular format is the Battle Royale mode which pits 100 players against each other, some of whom are in small teams, to see who is the last man standing.
News site Forbes said it had seen "dozens" of reports online by people who said their accounts had been compromised.
Many said they did not know how the hackers had got at their accounts.
The fraudulent payments made by the hackers appear to have been completed using payment details saved on the Fortnite game accounts.
Players have been hit by high charges for different versions of the Fortnite game as well as its online currency and cosmetic items for in-game characters.
Erik Kain, writing on Forbes, speculated that the attackers may have got at accounts because people re-used passwords across different services.
Recent data breaches had given attackers a ready-made list of possible passwords, he said, which they would then use against other services they were targeting.
In a statement, Epic said it was "aware" of the continuing attacks against players and the cyber-thieves were using "well-known hacking techniques".
It added: "Any players who believe their account has been compromised should reach out to our player support immediately."
At the same time, a row is brewing between Microsoft and Sony over letting players battle each other in Fortnite no matter how they access the game.
Soon it will be possible for PC, Mac and mobile players of Fortnite to take on people who access the game via console, and vice versa.
However, it will not be possible for Xbox or PlayStation owners to directly take each other on.
In a statement shared with technology news site Kotaku, Microsoft said it had offered to help set a system that bridged the divide between the two console populations but Sony had not responded to its offer.
Sony has yet to respond to a BBC request for comment about cross-console play.
In the past, reports the Verge, Sony has turned down offers to make cross-play work, citing safety fears.
The technical feasibility of PlayStation players fighting Xbox gamers in Fortnite was proven last year when technical problems briefly allowed the two groups to take each other on.