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Millions potentially affected by Yahoo Japan hack

Millions may be affected by Yahoo Japan hack

Yahoo's celebrations over its Tumblr purchase may be a little overshadowed by the news that it might have just lost a load of personal details from its Japan site.

22 million people's usernames may have been swiped in the attack, which took place on May 16, according to Yahoo.

"We don't know if the file (of 22 million usernames) was leaked or not," said in a statement. "but we can't deny the possibility given the volume of traffic between our server and external terminals."

Not so Yahoo!

Access to Yahoo Japan's services was suspended for several hours on discovery that a file containing the data of 22 million customers was found to have been potentially compromised.

22 million is a fairly sizeable chunk of Yahoo Japan's users - about a tenth - made even worse given that Yahoo is Japan's most popular search engine.

Usernames alone might not give hackers access to accounts but Yahoo Japan is still advising users to change their passwords. It also says that it's tightened its security to prevent any similar attacks from occurring.