Yahoo Japan said on Friday it suspected that up to 22 million of its user IDs may have been leaked.
Yahoo said it detected an unauthorized attempt to access the administrative system of its web portal Yahoo Japan.
According to Yahoo, the the leaked information did not include passwords and data necessary for identity verification to reset passwords, such as the "secret questions" asked by the network to users in order to change access their accounts without a password.
Previously Yahoo had been monitoring activity in its servers system in response to an unauthorized access occurred on April 2 in the Yahoo! JAPAN and the detection of suspicious logins to its servers.
Close To Tumblr?
Staying with Yahoo, the company called a press event in New York City on Monday afternoon, following the rumors that it plans to buy Tumblr for US$1 billion.
"Join us as we share something special," says the invite, sent to members of the press Friday afternoon.
Citing unnamed sources, All Things D reported earlier Friday that Yahoo may be in talks to partner with Tumblr, invest in it, or make an outright purchase.
If Yahoo's board signs off, the deal could be announced Monday.
Yahoo has said that Mayer will be on hand to unveil something related to a product.
Tumblr is offering stories, photos and other digital content served up by users who are connecting to the service through its mobile applications.