A South Korean researcher said Thursday that North Korea earns nearly one trillion won, or over 860 million U.S. dollars, each year from illegal cyber activities such as running gambling sites.

Yoo Dong-ryol, head of the Korea Institute of Liberal Democracy, made the remark during a cyber security conference hosted by the Defense Security Command.

Yoo said that a South Korean was arrested in 2013 for purchasing a gambling program manufactured in North Korea and bringing it into the South. He said that 15 North Korean nationals were also arrested in Cambodia in 2014 for operating an illegal gambling site.

The researcher said that money confiscated by the Cambodian police amounted to some ten billion won at the time. 

Yoo claimed that based on this information and other intelligence, North Korea is estimated to earn about an annual one trillion won from overseas-based illegal cyber activities.