About 3,000 cases have been discovered among users of site, with their IDs unknowingly being used to sell fake goods, the Yomiuri Shimbun reported Sunday.

An unnamed source said the total number of ID thefts may hit 10,000, with police receiving reports throughout Japan. In addition, many Yahoo Japan users are challenging company fees for transactions they say they did not initiate.

Yahoo is not yet accepting responsibility for the ID thefts on Japan's largest online auction service.

"An internal investigation we carried out hasn't found any information leakage. It can't be ruled out that the users themselves have had their IDs stolen as a result of (them entering their personal data via e-mail) phishing fraud schemes," said a spokesman.