Crooks have stolen and sold the personal information of over 90,000 Japanese Citi credit card holders.
The account numbers, names, addresses and dates of birth of 92,408 people was stolen although PINs and security codes were not taken.
No suspicious transactions have been spotted yet says the bank, which has called in the authorities and is contacting victims.
According to local press reports, Citi believes the data was not obtained by hackers but by someone at a third party vendor with access to the bank's systems.
In May crooks compromised details belonging to around 360,000 Citi North American credit card customers and are understood to have looted around $2.7 million from accounts.