SoftBank: a proxy server defect showed other customers' information in My SoftBank and swapped MMS sender identities

1. 2025-09-25

   It introduced the proxy server with the software that later caused the defect. [1]

2. 2026-01-13 09:47

   A network equipment configuration change raised how often the defect occurred. The same day, a customer who logged in to My SoftBank with line authentication reported seeing what appeared to be someone else's information. [1]

3. 2026-01-17 02:22

   The events stopped. The software has been fixed and the system now runs normally. [1]

4. 2026-01-19

   It found the cause: a software defect that, when many processes ran at once, could treat some customers as other customers. [1]

5. 2026-01-27

   It announced the events and reported them to the supervising authority. Affected customers are being contacted individually. [1] [2]

The events ran from 9:47 on January 13 to 2:22 on January 17, 2026. Counts were 2,019 cases of other people's information shown in My SoftBank and similar services, 2,209 cases of MMS sender swapped to someone else, 1,906 cases of MMS meant for others received (Android only), and 2,241 cases of +Message accounts switched to other people. Cases before the configuration change are estimated at up to 200. [1]

The information of other people that was shown included names, addresses, dates of birth, phone numbers, contract details and billed amounts. [1]