Toyohashi in Aichi Prefecture says citizens' email addresses may have leaked after a server run by a Tokyo contractor was illegally accessed. The contractor handles email delivery for My Number card procedures, the city said.
The breach occurred on October 28. It may have exposed the addresses residents registered when booking an appointment to collect their My Number card — the national ID number issued to every resident of Japan.
The city has stopped sending reservation confirmation emails and other messages until it confirms the system is safe. Officials urged residents not to open attachments or links in any suspicious email that arrives.
The incident is the latest to involve the data chain around My Number cards, which link tax, social security and identity records to a single number and are used for a growing share of administrative procedures.