Origin Energy (ASX:ORG) Chief Executive Frank Calabria said the firm had completed the initial phase of its ongoing review into a recent customer data security incident, which indicated that the information of around 900,000 current and former customers was accessed, according to a statement on Tuesday.

The firm had earlier said the impacted data potentially includes name, address, date of birth, contact phone number, and account information, as well as the last four digits of a credit card or the last three digits of a bank account.

Calabria apologized to the firm's customers and said it was contacting impacted customers and providing support. It extended its customer support hours and established a dedicated contact number for this incident. Origin is also working with cybersecurity and forensic specialists to ensure the incident is contained, he added.

It notified the Office of the Australian Information Commissioner regarding the matter.

Origin's shares fell nearly 2% in recent trading on Tuesday.