Japan’s Mizuho Bank, facing serious system problems since its launch in 2002, annonced on Wednesday the loss of confidential account data on 270,000 customers.

The retail banking unit of Japan’s biggest lender, Mizuho Financial Group, said data including customers’ names, account numbers and transaction histories had been lost at 167 branches in the course of several years.

The bank stressed that there was no evidence that the data had been leaked to outsiders or misused, according to the internal investigation.

“There is a high probability that the information was accidentally disposed of, and it is extremely unlikely that it was passed to outside parties,” the bank said in a statement seen by Reuters.

Mizuho has faced problems concerning system integration and data management since the retail unit was opened in April 2002 after the merger of three predecessor banks.

Customer confidence in Mizuho has been undermined since its first day in business, when difficulties in its network of 7,000 automated teller machines (ATMs) left thousands of customers without cash, Reuters reported.

The loss of the account data is the latest in a number of similar incidents that have alerted public in Japan to identity theft and other information-related crimes.