Kakao Corp., the operator of South Korea's dominant mobile messenger, has filed an administrative lawsuit against a government fine of 15.1 billion won (US$11 million) over the leaking of personal information on a large scale, according to sources Monday.

The Personal Information Protection Commission, the government's personal information watchdog, ordered the fine in May, concluding that Kakao's lax user data scrutiny and protection measures led to the data leak of some 65,000 users.

According to sources, Kakao challenged the fine order through the administrative suit filed on Nov. 1.

The fine was more than double the previous record fine of 7.5 billion won imposed on Golfzon, a screen golf business, by the watchdog.

Kakao previously stated that it would review various response measures, including an administrative suit, against the order.