Yahoo Japan Corp. released a statement last Friday warning that usernames of 22 million people may have been stolen in an attack on the 16th of May.
“We don't know if the file (of 22 million user IDs) was leaked or not,” said the company, “but we can't deny the possibility given the volume of traffic between our server and external terminals.” The attack was halted by cutting internet access to the company’s servers.
The company was also keen to stress that users’ data was not in danger, as the information leaked did not include passwords, or any of the details necessary for hackers to reset passwords.
Despite this, the hack is worrying for the company, especially in Japan where it is the top search engine, with a more than 50% market share. The company has advised users to change their passwords just in case, and has promised to tighten security in the future.