Monetary Authority chief executive Joseph Yam Chi-kwong yesterday urged the operator of the Octopus card system must determine how it over-deducted money from users' bank accounts or risk losing the public's confidence. The smart-card operator had also been asked to look beyond last week's incident and make sure it is able to respond quickly to emergencies, he told a radio programme. The firm, Octopus Cards, revealed last week that it had wrongfully deducted more than HK$140,000 from the bank accounts of some users who used EPS Add-Value Machines in MTR and KCR stations. EPS Add-Value services have been suspended since February 3, pending the results of an investigation into the glitch. Octopus Cards, a joint venture by major transport companies in Hong Kong, is governed by the Monetary Authority under the Banking Ordinance. 'It is necessary that they find out the cause of the fault, whether it was in the network, software or hardware,' Mr Yam said. Customer refunds should also be a top priority. 'We have asked them to investigate not only this particular incident but also how they manage what we call operational risk,' Mr Yam said. 'They cannot allow public confidence in their service to be doubted. It is very important.' Meanwhile, Mr Yam said he was not against more of the Exchange Fund, the reserves backing the Hong Kong dollar, being released in view of last year's surge in investment income. Although there was no definitive answer as to at what level the Exchange Fund should be kept at to protect the Hong Kong dollar against unexpected events, the issue warranted further examination, he said. 'I am not of the opinion that the entire HK$1.17 trillion [in assets] needs to stay where it is, and that we are to not move a cent. On this subject, I think we can research further, and I think the financial secretary would also keep an open mind,' he said. Mr Yam said he had already made his views known to Financial Secretary Henry Tang Ying-yen, who would make a decision based on the government's whole fiscal situation. He also urged investors to exercise proper risk assessment in the coming year. He cited rising uncertainty as investors riding recent years of economic growth became more likely to take risks. Combined with large-scale currency movements, Mr Yam said investing could be compared to a 'drunken man riding a roller coaster with no seat belt on'.