Up to 42,000 St George Bank customers have been sent printed statements containing the account information of other people after a "production issue" at vendor Salmat.
The Australian bank says that incorrect statements sent to some customers contains information such as transaction details and, in a small proportion of cases, account details that belong to another client. No PIN numbers are on the statements.
The error - affecting transaction and savings account statements with an end date of 26 February 2010 - happened after a "processing error caused a one-off interruption to an automated data processing function" at Salmat, a Sydney-based BPO firm. The firm blames human error when manually re-starting an automated production process.
St George is re-issuing correct statements and has set up a help line for concerned customers. Customers are advised to destroy any incorrect statement received.
The bank says it has "well established and highly sophisticated security measures in place to prevent customer accounts being inappropriately accessed at any time" but has heightened security measures.
Greg Bartlett, chief executive, St George, says: "We sincerely apologise to our customers for this error. This incident is totally unacceptable and we are treating it very seriously. I am overseeing this matter personally and we are committed to contacting each impacted customer."