The Tokyo Metropolitan Police Department has arrested six Chinese nationals on suspicion of unlawful confinement and attempted extortion involving a 23-year-old exchange student from China who had become involved in a financial dispute over a yami baito, or a “dark” part-time job, according to Jiji Press.

Yami baito are illegal employment schemes that lure individuals with promises of unusually high pay, but instead have them commit criminal acts, usually involving activities such as handling money obtained through fraud or burglaries.

Often run by tokuryū, or “anonymous fluid criminal groups,” perpetrators leverage social media to recruit participants into yami baito schemes and communicate with them via encrypted messaging apps.