Seoul police have uncovered six companies accused of mass-sending phishing messages beginning with “international sender” under the direction of criminal organizations, authorities said Thursday.

After investigating the six firms from May to October this year, police sent 20 individuals -- among them a key operator named Kim, his employees and system developers – to the prosecution on charges of violating the Telecommunications Business Act and the Information and Communications Network Act.

The police found that these six firms sent an estimated 2.8 billion spam messages, earning between 14 and 20 won per message, from 2015 to 2023. Given that there were approximately 569.2 million local mobile subscribers as of August, this equates to an estimated 50 spam messages per subscriber. Altogether, these firms amassed around 48.5 billion won ($35 million) in illicit profits.

Police are working to freeze assets worth about 4.9 billion won, including Kim’s cash holdings and virtual assets totaling 4.8 billion won.

While mass text message service providers are required to register with the government, these firms circumvented legal oversight by routing messages through overseas telecommunications networks.