A US mum has written a Facebook post describing her shock at seeing her child's avatar being "gang raped" by others in the online game Roblox.
Amber Petersen said her seven-year-old was playing the game, which is marketed at children, when she showed her the screen and asked what was happening.
She also shared screenshots, which showed two male avatars attacking her daughter's female character.
Roblox said it had banned the player who carried out the action.
Ms Petersen said in her post that she felt "traumatised and violated on so many levels" following the experience.
The screenshots she shared included a representation of male genitalia.
"Parents/Caregivers... not only do I urge you to delete this app, I hope you will take another look at all of your devices and their security settings," she wrote on Facebook.
Roblox said it was "outraged" that a "bad actor" had violated its community policies and rules of conduct.
"We have zero tolerance for this behaviour," said a spokesperson.
"Our work to ensure a safe platform is always evolving and remains a top priority for us."
Roblox is a popular multiplayer game marketed at children and has been compared to Mojang hit Minecraft.
Players can create their own games and also join in games created by others.
It has a 7+ age rating from European classifier Pegi (Pan European Game Information) and a 10+ rating from the ESRB (Entertainment Software Rating Board) in the US.
It has been around for 14 years and claims to have 64 million monthly players.
The UK Safer Internet Centre has a blog post containing guidance for parents whose children play Roblox.
They include activating the additional safety features for children aged under 13 and showing an interest in the games they play.