Australian Securities and Investments Commission chairman Joe Longo has warned businesses must close “alarming” gaps in their cybersecurity defences, while experts said it would be “very costly” for telcos to comply with new cyber laws foisted on them after Optus’ network outage last week.

Mr Longo was speaking as the regulator released an annual snapshot of corporate Australia’s cyber preparedness on Monday, which found almost half were not managing third-party or supply chain risks, commonly used by hackers to breach companies.