Mainichi Newspapers: credential stuffing on Mainichi Shimbun Digital logged into 21,752 IDs in three days, with no sign that personal data pages were viewed

1. 2025-07-08

   A flood of login attempts began. [1]

2. 2025-07-10

   In the morning it detected suspicious access to the system that checks login details, and at night it restricted outside access. [1]

3. 2025-07-11

   It announced the incident, invalidated the passwords of the IDs that logged in and asked members to reset them. It also consulted the police. [1] [3]

4. 2025-09-11

   It published its findings. The IDs that logged in numbered 21,752 between July 8 and 10, and the method was a list attack using IDs and passwords that may have leaked from other services. [2]

There is no sign that the personal data page of member accounts (address, name, phone number, gender, date of birth, payment method) was viewed, and no leak was confirmed. Card data is held in a separate system. The email addresses used in the attempts included many that were not registered with Mainichi Shimbun Digital. [1] [2]