Benesse Holdings Inc. has learned of a new customer data leak at an education service unit, after the company was the target of Japan's largest-ever data theft scandal last year.

A temporary employee at Transcosmos Inc., a Benesse Corp. subcontractor for call-center operations, illegally acquired personal data for 23 customers when he was allowed to access the data between March and August last year, Benesse Holdings said on Tuesday.

The stolen data were not leaked to a third party, it said.

This is the latest setback for the major Japanese education business company following the arrest of a system engineer employed on a temporary basis at an affiliate. That temporary worker is suspected of stealing data for some 40 million Benesse customers to sell to third parties.

The new leak was found after the Transcosmos temporary employee in his 30s was arrested over a different crime. Transcosmos dismissed him on Jan. 28.

The Ministry of Economy, Trade and Industry asked Transcosmos to report by Tuesday details of the incident and measures to prevent a recurrence.