Data allegedly stolen by a 39-year-old former systems engineer from the Benesse group was sold to at least 14 name-list traders, investigative sources said Thursday.
The massive amount of customer data might then have been resold to a few hundred companies, the sources said.
Tokyo prosecutors on Thursday indicted the former engineer, Masaomi Matsuzaki, for violating the Unfair Competition Prevention Law.
He allegedly downloaded and copied the data covering about 10 million customers onto his smartphone June 17 at an office in Tokyo of an affiliate of Benesse Holdings Inc., a leading correspondence education provider for children, according to the complaint.
Matsuzaki was arrested last month in the largest-ever private data leak scandal in Japan, prompting the government to seek revisions in the Personal Information Protection Law, a government source has said.
Tokyo police plan to issue another arrest warrant on Matsuzaki on suspicion of stealing data related to another 20 million customers, the sources said.
Matsuzaki told the police he sold the data to three name-list traders in Tokyo, one of which told the police it resold the data to about 50 companies such as cram school operators, kimono shops and photo studios, the sources said.
The data obtained by another name-list trader, which said it sold the data more than once, were sold to Tokyo-based name-list trader Bunkensha through several other such traders and eventually purchased by software developer Justsystems Corp., which said last month it bought data from Bunkensha in May.
Benesse's customer data were leaked to English conversation school operator ECC via other traders. ECC has said that some of the data it bought from a company possibly came from Benesse.