Yahoo!’s security nightmare shows no signs of letting up. Following reports earlier this month the the company is unable to protect its customer’s email accounts from being hacked and used to send massive amounts of spam, it’s Japanese subsidiary has suffered an equally embarrassing breach.

Reuters is reporting that Yahoo! Japan has had to ask more than 200 million customers to reset their passwords after detecting an intrusion in one of its main servers last week. The company believes that more than 22 million user IDs may have been exposed.

Reuters says that a suspected intrusion was first discovered on Thursday night, local time, causing Yahoo! Japan to suspend access to its services for several hours whilst investigators checked what had happened. An investigation later revealed that a file containing the personal data of 22 million customers had potentially been compromised.

“We don’t know if the file was leaked or not, but we can’t deny the possibility given the volume of traffic between our server and external terminals,” said a spokesperson for Yahoo! Japan in a statement delivered to AFP.

Yahoo! Japan didn’t reveal any other details about the hack, except to insist that the compromised file didn’t contain any user passwords. Nevertheless, the fact that it’s asking users to reset their passwords would suggest that whatever data the file did contain could well be used to compromise its user’s accounts.

The latest breach will do little to generate confidence in Yahoo!’s already questionable security systems. ABS-CBN News reported a similar breach last April during which unknown hackers “came close” to stealing the email addresses and passwords of more than 1.2 million user accounts.

Even more worrying is Yahoo!’s apparent inability to protect its Yahoo! Mail servers. As SiliconANGLE revealed earlier this month, hundreds of Yahoo! Mail accounts have been compromised since the turn of the year, apparently by hackers based in Russia. The hackers employ a technique that exploits a cross-site scripting (XSS) vulnerability in Yahoo!’s email service, allowing them to take control of people’s accounts and bombard their contacts with “get rich quick” spam.

Yahoo! first acknowledged the problem in January, before immediately claiming the vulnerability had been fixed. However, customer complaints have continue unabated. SiliconANGLE has since made several attempts to contact Yahoo! seeking reassurance that its working to fix the problem, yet the company has repeatedly ignored our messages, something that would suggest it is unable to find a solution.