Lee headed Kakao Corp., the original provider of the popular messenger app Kakao Talk, before his company merged with Daum Communications Corp., South Korea's second-largest portal operator, in October.

All online service providers are obliged to take due measures to identify child pornography on their networks, according to South Korean law.

This marks the first time that the head of an online service provider has been investigated on charges of violating laws on child pornography in South Korea.

The move came after the police asked prosecutors to indict a 20-year-old man, identified only by his surname Jeon, for sharing massive amounts of child pornography through Kakao Group earlier this year.

Jeon allegedly distributed sexually explicit videos of children through multiple Kakao Group accounts he created from June to August, police said.

More than 10,000 people were part of these groups, with over 80 percent being teenagers, a police official said. Some of these young users are believed to have shared pornographic videos they took themselves.

"I understand child pornography is being shared rampantly on the social networking service," a source within the police agency said. "It seems like Kakao didn't take any action to filter out materials considered to be child pornography."

Fifteen teenagers were found to have created similar groups as Jeon, but were released on the condition that they seek therapy and psychiatric treatment. (Yonhap)