Japan’s Mizuho Bank, plagued by system problems since its launch in 2002, said on Wednesday it had lost confidential account data on 270,000 customers.

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

The bank said an internal investigation had uncovered no evidence that the data had been leaked to outsiders or misused.

“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.

Mizuho has struggled with problems related to system integration and data management since the retail unit’s launch in April 2002 following the merger of three predecessor banks.

Customer confidence in Mizuho has suffered since its first day in business, when glitches in its network of 7,000 automated teller machines (ATMs) left thousands of customers unable to withdraw cash and others charged with double deductions.

Full integration of Mizuho’s computer network and other systems has still not been completed.

Mizuho has some 30 million account holders, the most of any Japanese bank.

The loss of the account data is the latest in a string of similar incidents that have raised public concern in Japan about identity theft and other information-related crimes.

Last year, data on 4.52 million subscribers to Japan’s largest provider of broadband Web access, Softbank Corp.’s Yahoo BB Internet service, was leaked to criminals.

Police later charged four men with trying to extort money from Softbank by threatening to circulate the data.