Former NSW Premier and Optus senior executive Gladys Berejiklian has lost her bid to overturn findings of serious corrupt conduct.

Fees paid to the directors of Singtel – the owner of Optus – have soared by more than 80 per cent in just one year.

Telco giant Optus runs a “world-class” global cyber security business but is refusing to say whether it was used to protect its Australian customers, the group’s biggest source of profit.