The worst global IT outage in history — which shut down airlines, banks, supermarkets, hospitals and businesses from Australia to the US — could take “some time” to fully rectify, says CrowdStrike, the cybersecurity firm behind the crash.

More than 4200 flights were cancelled globally, media outlets stopped broadcasting, hospitals could not treat patients, and government services were left scrambling by the meltdown that was first noticed in Australia after 3pm (AEST) on Friday.

The massive outage was caused by a bug in a basic software update on virus scanner Falcon, by cybersecurity firm CrowdStrike, that hit Microsoft operating systems.

Users worldwide running Windows software reported computers flashing  with the dreaded blue screen of death.

CrowdStrike chief executive George Kurtz apologised in a television interview on NBC and explained that although they had “resolved the issue” it might take time for systems to reboot.

“We’re deeply sorry for the impact that we’ve caused to customers, to travellers, to anyone affected by this, including our companies,” said Kurtz.

“It could be some time for some systems that just automatically won’t recover, but it is our mission… to make sure every customer is fully recovered.”

Microsoft suggested on its website to reboot systems up to 15 times, by turning them on and off again.

Businesses started falling like dominoes about 3.30pm on Friday around the world, including Australia, the United States, New Zealand, Germany, Switzerland, Israel, Philippines and South Africa.

Jetstar cancelled all Australian flights, with hundreds of people left stranded at airports. Jetstar said flights would resume on Saturday (July 20).

Qantas and Virgin Australia, as well as police forces across much of the country and the federal and NSW governments were also hit.

Point-of-sale machines at shops including Coles and Woolworths were unable to process customer transactions, forcing at least six Woolworths stores to shut.

Shoppers were forced to leave trolleys full of goods abandoned at supermarket registers.

Crowd-sourced website Downdetector listed Telstra, Microsoft, Google, Foxtel, National Australia Bank, ABC, Uber, ANZ, and Bendigo Bank as suffering outages.

Many media organisations were impacted.

“The ABC is experiencing a major network outage, along with several other media outlets,” it said in a news story.

Nine and Sky News said its news bulletins were affected.

Even footy fans were being hit, with AFL club Essendon warning them to bring physical tickets so they could get into Marvel Stadium on Friday night.

Global victims included Paris Disneyland and other theme parks, Britain’s National Health Service and major international airlines.

The financial costs are expected to be tallied by economists over the weekend as they estimate the money lost to businesses.

A New York City subway line affected by the outage. Photo: Getty

While many breathed a sigh of relief that hackers were not responsible, cyber security experts warned the incident exposed a soft and exposed belly of the country’s IT systems.

“It’s not just a mistake or just an error; this is the worst sort of thing that can happen,” cybercrime professor Richard Buckland, from UNSW’s School of Computer Science and Engineering, said.

“This is more serious than a cyberattack because it shows our systems aren’t even proofed against randomness.”

Monash University cybersecurity professor Nigel Phair described the incident as “unprecedented in scale” and said the outage highlighted the dependencies organisations had on the internet and related online technologies.

The system failure forced the federal government to convene a snap crisis National Co-ordination Mechanism meeting on Friday evening.

“Crowdstrike attended the meeting and we can confirm there is no evidence that this is a cyber-security incident,” Home Affairs Minister Claire O’Neil said on Friday night.

“This is a technical issue, caused by a Crowdstrike update to its customers.”

The company said it had issued a fix for the problem, allowing affected companies and organisations to reboot their systems.

–with AAP