A Greek Australian family appears to have fallen victim to identity theft following the recent Optus telecoms hack which saw thousands of customer data breached, resulting in them losing some $40,000.

Appearing on the Today Show, Jimmy Marinis and Mary-Jane Daffy said they believed identity thieves "piggy backed" off the Optus hack and gained access to their bank accounts, emptying out their credit cards along the way.

Marinis told the Today Show that several transactions had been made, accounts had been opened, personal loans had been applied for under their names and their credit cards were drained.

The pair run a small business together and Mary-Jane said the whole ordeal "felt like watching your house slowly burn to the ground".

"I think it's incredibly paralysing," she said.

"In real time you are watching your money getting siphoned out of your bank account or loan applications, credit applications, new phones being taken out in your name, numbers being changed. The list goes on."

Optus hack: What customers need to know right now

Optus services, including mobile and home internet, are not affected, and messages and voice calls have not been compromised. Optus services remain safe to use and operate as per normal.

“Optus has also notified key financial institutions about this matter. While we are not aware of customers having suffered any harm, we encourage customers to have heightened awareness across their accounts, including looking out for unusual or fraudulent activity and any notifications which seem odd or suspicious.”

To help protect against fraud, customers are encouraged to look to reputable sources such as:

• moneysmart.gov.au/banking/identity-theft
• Identity fraud - Home (oaic.gov.au)

For customers believed to have heightened risk, Optus will undertake proactive personal notifications and offer expert third-party monitoring services.

The most up-to-date information will be available via optus.com.au. Customers who have specific concerns, can contact Optus via the My Optus App (which remains the safest way to interact with Optus) or by calling 133 937. Optus will not be sending links in any emails or SMS messages.