New Zealand's Banking Ombudsman has warned customers against using unsecured Wi-Fi networks when doing their online banking after a New Zealand couple lost hundreds of thousands of dollars to fraudsters who picked up their details through such a network.Ombudsman Deborah Battell said the couple had put a six-figure sum on term deposit with a New Zealand bank and had then used a Wi-Fi network at an American airport to access their email.The couple had stored their banking details, including documents with signatures, in their email accounts, which were then picked up by a fraudster and used months later to withdraw the money from the account online, Battell said.The fraudster found separate emails with bank account details and one with a signed employment contract."This ultimately enabled the fraudster to pose as one of the customers and successfully email instructions to the bank to transfer funds out of the couple's account," Battell said. "The fraudster was able to make the email look as though it had come from the couple's address and fooled the bank into thinking it was genuine," she said.The un-named bank agreed to the emailed request. However, an inquiry later found its practices were out of line with the rest of the industry. Some banks refuse to accept email instructions, while others accept emailed requests but only after they have verified the customer's identity directly through a phone call and a series of security questions.The bank involved has now changed its practices around emailed requests, Battell said.The Banking Ombudsman found in favour of the couple and the bank had reimbursed the couple for their fraudulently withdrawn funds.