Yahoo Japan said it detected an unauthorised attempt to access the administrative system of its web portal site and suspects that about 22 million of its around 200 million user IDs may have been leaked.

The Kyodo news agency reported that the leaked information does not include passwords and user data necessary for identity verification to reset passwords.

The company has checked its system after severing access and found traces of an attempt to steal user IDs, the news agency said.

Yahoo Japan is the joint venture between SoftBank, which owns a 35.5% stake, and Yahoo, which owns a 34.7% stake.

Kyodo News reported that earlier this year a hacker had gained unauthorised access to a system managing the Yahoo Japan portal website and was close to stealing information that included IDs, e-mail addresses and passwords of about 1.27 million accounts.

Last year, it was reported that about 500,000 usernames and passwords from a Yahoo service have been hacked and posted online.

A previously unknown hacker group called D33DS Company claimed responsibility for the hack.

The latest hacking comes following news that Yahoo is nearing the acquisition of blogging and social networking site Tumblr for $1.1bn.