A cyber security expert says Optus customers should be on high alert for potential scam calls and emails after a major data breach on Thursday.

CyberCX chief strategy officer Alastair MacGibbon told Michael Genovese, in for Gareth Parker on 6PR Breakfast, the massive data breach from Australia’s second-largest telco was concerning, with the personal information of millions of customers potentially compromised.

The attack exposed passport details, driver’s licence and phone numbers, email and home addresses and dates of birth of 2.8 million customers.

A further 7 million Optus users had their dates of birth, email addresses and phone numbers stolen.