A total of 100 messages with virus-infected files were sent simultaneously to email addresses given to Japan Pension Service staff, and police suspect that led to the recent massive leak of personal data, sources said Wednesday.
None of the email addresses had been disclosed to the public, and there is a possibility they had been obtained by hackers who previously attacked the organization's system using computer viruses.
The initial attack, on May 8, was made using an email sent from a free account to the pension body's public address, the sources said. The email contained external links.