Origin Energy believes the information of approximately 900,000 current and former customers was accessed during a recent data security breach.The energy provider confirmed it first became aware of a potential security threat in early July but initially did not believe it credible.The company has urged customers to be vigilant to scams and said specialist identity and cyber support services were available to affected customers."We have now completed the initial phase of our review into Origin's customer data security incident," Origin chief executive Frank Calabria said in a statement.Customers whose information has been accessed will be contacted, Origin said, and customer support hours extended."We are working with cyber security and forensic specialists to ensure the incident is contained, and we've taken a number of steps to secure our system," Mr Calabria said, confirming Origin was working with government and other agencies, and continuing its review into the incident.Origin said it had been reviewing a "potential security threat" since early July."We worked to confirm its credibility and potential impact; however, based on the information available, it was not assessed to be credible," the statement said."On 22 July, new information emerged that indicated a potential security incident may have occurred."We acted immediately, providing updates to the market and notifying our customers as a precaution."Mr Calabria said it was a "criminal matter" that was now being investigated by the relevant authorities."Given this, we are constrained by the level of information we can provide about the incident at this time," the chief executive said.Shares in Origin Energy were down more than 2 per cent by 11am AEST on Tuesday.