Optus customers are being warned to be extra vigilant after hackers breached the telco’s systems in what’s thought to be one of the largest cyberattacks in Australian history.

Optus has not revealed how many customers have been impacted, but a source has told The Age up to nine million current and former customers may be affected.

Data exposed includes names, dates of birth, phone numbers, email addresses, and for some customers also addresses ID documents including driver’s licences and passport numbers. Payment details and account passwords have not been compromised.

Press PLAY below to hear a tech expert’s warning to current and former Optus customers

Tech expert Geoff Quattromani says the breach is “significant”.

“If you’ve had an Optus service there’s a pretty good chance your data is now in someone else’s hands,” he told Tony Jones, filling in for Ross and Russel.

Mr Quattromani urged current and former Optus customers to be extra vigilant.

“A lot of the information that’s out there, our date of birth and those sorts of things, that’s always going to be current data,” he said.

“You need to start paying attention to your bank … start paying attention to your email.”

The risk of identity fraud is also something Optus customers should be aware of.

“When we lay out all of those different factors that they’ve taken, that’s 100 points of ID. That’s enough to sign up for a credit card, a mobile phone service,” Mr Quattromani said.