22 million user IDs may be in the hands of hackers, after Yahoo Japan security breach

The call has gone out to Yahoo Japan’s 200 million users to change their passwords, after the company warned that it suspected hackers had managed to access a file containing 22 million user IDs.

Yahoo Japan says that it detected an attempt to gain unauthorised access to its administrative systems on Thursday at approximately 9pm local time.

Although the information taken from Yahoo Japan’s servers is said not to contain passwords, or other personal identifying information required to hijack an account (such as the answers to secret questions), the site has decided that users should reset their passwords regardless.

In a press statement published on Yahoo Japan’s website, the number one search engine in Japan stressed that it had not confirmed that the data had definitely leaked to the outside world, but that it deeply apologised for any inconvenience caused…

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Read more in my article on Sophos’s Naked Security blog.


Graham Cluley is an award-winning keynote speaker who has given presentations around the world about cybersecurity, hackers, and online privacy. A veteran of the computer security industry since the early 1990s, he wrote the first ever version of Dr Solomon's Anti-Virus Toolkit for Windows, makes regular media appearances, and is the co-host of the popular "Smashing Security" podcast. Follow him on Twitter, Mastodon, Threads, Bluesky, or drop him an email.

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