The breach involved the theft of personal information belonging to more than 2.58 million individuals, alongside the email passwords of 54,401 users, according to the company's announcement.
So-net operates as a Japanese internet service provider under the Sony Group. The company stated in a notice that "We have confirmed an information leak caused by unauthorized access to the member database."
The security incident was detected four days after occurring on October 19, leading the organization to shut down the affected servers and block external communication.
The investigation confirmed that 2,585,481 customer records were exposed. Notably, no banking, payment card, or other account details were compromised.
The exposed records include 2,141,986 So-net entries and 443,495 plala (S Course) records, which relates to NTT Docomo’s Docomo Hikari services.
NTT Docomo also alerted its clientele, warning about phishing emails and fake websites related to its d POINT Club and a Universal Studios Japan (USJ) campaign.
Sony reported the incident to Japan’s Personal Information Protection Commission and is currently investigating its scope and cause. As of October 27, neither entity had confirmed any misuse of the exposed data externally.
This incident contributes to a trend of escalating cyber threats in Japan, where numerous high-value companies and providers have recently been targeted.
The continuous rate of data breaches presents a significant threat, prompting the Japanese government to hold urgent meetings to plan countermeasures.
