At least 303 cases of unauthorised access were confirmed between late May and June 14, including three that involved cash trades resulting in financial loss, a Line spokesman told AFP, without providing further details.
"We are cooperating with police in investigating the cases, and we are calling for users to change passwords," the spokesman said.
The accounts were hacked "presumably after shared passwords with other online services were leaked somewhere else," he said, adding that to the company's knowledge, all of the breaches occurred in Japan.
Another spokeswoman for the company stressed that Line's servers had not come under attack.
"Line's system itself has suffered nothing abnormal. It is not that our system was hacked," she said.
A police spokesman said the case was under investigation.
AFP