A cyber security experts says it's possible some Australian organisations have been affected by a global malware attack but are staying tight-lipped.
The so-called ransomware has wormed its way into thousands of computer systems in an apparent extortion plot, shutting users out unless they coughed up a payment.
Cyber Security Minister Dan Tehan said Australian organisations do not appear to have been affected.
"There has been no impact on the Australian health system at this stage," he told reporters on Saturday.
But University of Melbourne computing expert Dr Suelette Dreyfus believes it was possible local organisations had been hit, only they're keeping it under wraps.
"It might be that they're just being very quiet because they don't want to instil a lack of trust in their system," she said.
Dr Dreyfus said Windows computers that don't have the latest security patches were vulnerable to the bug, urging Australians to ensure their antivirus software was up to date.
"Every institution, every consumer, every student with a laptop should make sure that their system is fully patched," she said.
"Because this would be nowhere near the international spread and depth of attack if people had run the updates that Microsoft had provided in March."
The attack struck at least 16 British National Health Service organisations, along with computer networks of companies and municipalities in dozens of other countries.
Several hospitals in London and other parts of England and Scotland were affected and some reportedly halted surgeries amid fears the lives of patients were at risk.
"It's an international attack and a number of countries and organisations have been affected," British Prime Minister Theresa May said.
More than 75,000 similar attacks reportedly happened in almost 100 countries, with Russia, Ukraine and Taiwan hardest hit, according to the cybersecurity firm Avast.
Spanish telco giant Telefonica and US delivery service FedEx were among the businesses affected.
Prime Minister Malcolm Turnbull said the government was monitoring the situation closely.
The ransomware known as Wanna Decryptor is believed to be responsible.