A magnetic tape kept in Singapore that contains information on 123,690 customer accounts at Citibank's Japan unit has been missing since last month, officials at the Japan arm of the U.S. bank said Friday.
They said it was not immediately known whether the data have been leaked to a third party. Citibank will send a written apology and explanation the each customer whose information is missing, the officials said.
The bank's Japan unit said, "We will review our management process so that such an incident will never occur again."