Earlier this week a computer security researcher revealed that information about 3.3 million Sanrio Town members was accessible.
The Japanese firm Sanrio, which owns Hello Kitty and runs Sanrio Town, said it had now closed the loophole.
It added that no information about Hello Kitty fans had been stolen.
It added that only personal information, including names, email address and encrypted passwords, had been available to those who knew where to find the servers.
Information on more than 180,000 children was in this cache. No credit card or payment information was held on the vulnerable servers.