NetBank still reeling from cyber attack

Customers say they have been blocked from seeing their past transactions, making routine business difficult to conduct.

In a notice to its 2.5 million NetBank customers, CommBank said it had "identified that some transactions completed between March 27 and June 29 are not displaying on some accounts within NetBank ... Please be assured that your account balances are correct, and we aim to resolve this shortly".

The bank has given no date for resolving the problem.

Bill McKelvey of Mt Beauty Property Sales in Victoria said he needed an open record of recent transactions for his work.

"I can access what is paid in over the last two or three days," he said, but "the whole three-month chunk is missing [on NetBank". He said he would have to wait for his printed statement to confirm past transactions.

CommBank said it was still analysing some of the data that formed a 66 per cent spike in traffic on Monday, and that it was probably a denial-of-service attack by hackers. Such attacks involve flooding a computer with malicious data to knock it offline. The malicious data, now quarantined by CommBank, "was coming from offshore", its chief information officer, Michael Harte, said.

"We still don't know the origin of it and why there would be such large volume," he said. "We're doing further forensics [on the suspicious emails] to make sure we're absolutely safe."

CommBank said no customer accounts were compromised and no customers would be out of pocket.

An information technology professor, Jill Slay, said denial-of-service attacks were becoming common but she had not seen this kind of dual attack on a bank in Australian before.