During the pandemic, unofficial fan-run versions of a children's game called Club Penguin surged in popularity.
But a BBC investigation found one site to be a breeding ground for "e-sex", racism, bullying and anti-Semitism.
Disney is now threatening legal action to get the site and all other Club Penguin clones shut down, and one man has been arrested on suspicion of possessing indecent images of children.
Cyber-security reporter Joe Tidy reports.
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