Private customer data held by Australia's financial institutions is being sold over the so-called "dark net" according to Insurance Australia Group chief executive Peter Harmer, who has warned cyber attacks could wipe hundreds of millions of dollars off the value of some of our largest banks and insurers.

Mr Harmer says the insurance giant is attacked 60 times every day and that any chief executive who believes they have a secure digital environment is "completely oblivious to the threats that are out there".