Blackmailers attempted to extort almost $90,000 from one of Japan's largest phone companies by threatening to reveal a leak of private data belonging to four million customers before a major shareholder meeting, according to local press reports.

Two men have been arrested by Tokyo police investigating the case, the Asahi Shimbun reported yesterday.

The alleged extortion attempt involved the personal contact details of nearly four million customers of fixed-line internet services operated by KDDI Corp. 

As well as contact information, other identifying information such as gender and date of birth were copied from tens of thousands of customer records.

In the past, this kind of data has been used to swindle individuals and financial institutions out of large sums of money in identity theft cases.

KDDI apologised for the privacy breach in a news release, stating that it would review internal procedures to prevent a recurrence. Account passwords had not been stolen, the company stressed.

The blackmailers allegedly revealed the existence of CD-Rs and USB Flash memory sticks containing the customer data to KDDI officials on 30 May.