Seiyu: an attack on the shift scheduling tool of US vendor Blue Yonder leaked employee IDs, names and birth dates of 30,508 current and former staff

1. 2024-10-15

   Blue Yonder was hit by an external cyberattack. The attack period ran to October 24. [1]

2. 2025-10-30

   Seiyu and Trial Holdings announced that employee data had leaked from Blue Yonder's shift scheduling tool "Work Force Management". [1] [2]

The affected are 30,508 current and former Seiyu staff whose data was stored on Blue Yonder's systems during the attack period (provisional, as of October 28, 2025). Employee IDs and kanji names of all 30,508, birth dates of 26,353, and start dates, employment types and attendance codes of all 30,508 leaked, along with initial passwords of 7 people. Ordinary customer data was not included. No secondary harm has been confirmed. [1] [2]

Starbucks Coffee Japan has also announced an employee data leak involving the same Blue Yonder tool. [2]