Yahoo Japan is in hot water for the slack handling of people's personal information. The communications ministry says the web giant handed smartphone data to a third party without due notice, and must improve.
On Wednesday, government officials ordered Yahoo Japan to tell users in advance when providing their location data to another firm.
They say the information was taken from people's smartphones between May and July, and handed to South Korean firm Naver, which was able to replicate the data freely.
The officials told Yahoo Japan to ensure user information cannot be copied.
The firm is required to submit a progress report to the ministry by September 29.
Yahoo Japan has apologized, and pledged to act more responsibly.