Unauthorized access to Iwai Cosmo Securities led to trades in about 1.25 million shares that customers never intended, the brokerage's chairman said at a news conference on Friday, apologizing for the breach.
Chairman Okinotsu disclosed the figure for the improper trading at the briefing. He offered the company's apology to customers affected by the incident.
The source does not say how the access was carried out, when the trading took place, which accounts were affected, or whether customers lost money as a result.
The case points to a risk that sits close to household savings: an online brokerage account can be used to place orders its owner did not make. Similar concerns surfaced the same day in a separate alert over unauthorized access to a GMO FX trading server, where customers reported suspicious account activity.