Japan's communications ministry has given the operator of the Line messaging app administrative guidance in response to the apparent leak of more than 510,000 items of users' personal data.

LY Corporation revealed last November that about 440,000 items may have been leaked, due to a cyberattack on a subcontractor of the South Korean IT firm Naver. The figure was raised to 519,000 last month.

On Tuesday, a communications ministry official handed LY President Idezawa Takeshi a document and asked the company to make sure there are no further data leaks.

Idezawa apologized for causing so much trouble and vowed to take steps to prevent a recurrence.

Communications minister Matsumoto Takeaki told reporters on Tuesday that his ministry will step up surveillance. He suggested that the ministry will take tougher measures, if there is no improvement and similar leaks occur.

Matsumoto said the ministry will ask LY to provide information on the steps it is taking.

The operator of Line had been asked to tighten data control when it was revealed in 2021 that engineers for a Chinese company, to which Line had outsourced system management, had access to users' personal data that is stored in a server in Japan.