On Tuesday evening, Yahoo Japan (owned by Softbank) notified the public that they have discovered malware on their servers, which was intent on extracting data about over a million users, but was luckily detected in time and blocked from exfiltrating it to remote servers.
Users of Goo had no such luck, as the portal login page was bombarded with over 30 login attempts per account per second as the attackers tried to brute force their way into user accounts.
According to the company that owns and runs the site, they managed to access some accounts.
Since the portal offers email, search and online shopping services, and the accounts contain users' financial information such as credit card numbers and security numbers, the company has rightly decided to look some 100,000 accounts for the moment in order to prevent unauthorized access.
Both companies are investigating the attacks, but there is still no word on whether they are linked.