TOKYO : Yahoo Japan Corp. has said it suspects up to 22 million user IDs may have been stolen during an unauthorised attempt to access the administrative system of its Yahoo! Japan portal. “We don’t know if the file (of 22 million user IDs) was leaked or not, but we can’t deny the possibility given the volume of traffic between our server and external” terminals, the company said in a statement late Friday. The information did not include passwords and the kind of data necessary to verify a user’s identity or reset passwords, it said.