Yesterday, a software update grounded planes, impacted emergency services and stopped TV. So how did this actually happen?

"Your PC ran into a problem and needs to restart."

Splashed across the dreaded blue screen, these are the words no one wants to see pop up on their computer. 

But yesterday, millions of devices displayed the "blue screen of death", after what experts have called the "greatest global IT outage of all time". 

The outage impacted health and telco providers, media websites, banks, supermarkets and airlines around the world, and saw many organisations descend into chaos as they grappled with the catastrophic impact of a technology pause.

Watch: 'Deep Fakes' Are Becoming More Realistic Thanks To New Technology. Article continues below. 

Who, or what, caused the IT outage?

While many assumed the outage was the result of a cyberattack, the global havoc was caused by something far less sinister.

It all came down to a company you've probably never heard of launching a routine software update. That update had a bug in it, causing an issue with the Microsoft operating system, and it brought the millions of computers using the software to a standstill. 

The company is CrowdStrike, a cybersecurity firm based in Texas, USA. The organisation offers cloud-based online security solutions to big businesses, including airlines and banks. 

CrowdStrike also manages endpoint protection, antivirus capabilities, real-time monitoring, and threat detection to prevent unauthorised access, and protect customers from hackers and breaches.

The company is one of several that provide similar security software, usually to larger organisations. More than 23,000 worldwide companies are subscribed to CrowdStrike, and although its software impacts millions of end-users, most wouldn't have heard of the company that has around 8000 employees and turns over around $3 billion in revenue every year. 

So, what actually happened? 

Basically, CrowdStrike uses a platform called Falcon, purpose-built to stop breaches and protect from attacks including credential theft. The platform is installed on Windows, Mac and Linux systems. 

CrowdStrike launched a software update earlier this week, but the update had a bug in it, wiping out Microsoft's operating system, and ultimately causing global chaos. 

"Today was not a security or cyber incident. Our customers remain fully protected," CrowdStrike CEO, George Kurtz said in a statement.

"We understand the gravity of the situation and are deeply sorry for the inconvenience and disruption. As noted earlier, the issue has been identified and a fix has been deployed."

Who was impacted by the tech outage?

Thousands of people were impacted by the outage that brought multiple organisations from across the globe to a grinding halt. In Australia, the outage impacted media websites, banks, airlines and supermarkets. 

Several flights were delayed or cancelled, with Jetstar being the most impacted by the outage. Supermarkets continued to trade, but some checkouts were closed and lines were longer than usual. Some online orders weren't fulfilled. 

Systems were down at many grocery stores. Image: AAP.

Payment systems caused disruption at fuel stations too. Services including Online Shop, Post BillPay online, MyPost Business online, Mail Redirection Service Online, National Police Checks, and PO Box Lease & Renewal online, were also impacted, as were some police and fire systems. 

Globally, the impact was even more dire. 

According to aviation analytics firm Cirium, more than 3300 flights were cancelled around the world. Non-urgent surgeries were cancelled in several countries, with hospitals and medical centres having major problems with their systems. 

Emergency services were impacted in many countries too, including America's 911. 

Several TV stations in the US were also prevented from airing local news early on Friday, and even Australia's Sky News was impacted.

Plus, multiple supermarkets were only able to accept cash — something most people don't carry these days. 

Banks and betting agencies were hit too, and the London Stock Exchange was down for four hours. 

What happens now? 

While the software defect has been fixed, some systems were unable to reboot to receive the update. That means, the fix will need to be implemented manually, which could take a while. 

Crowdstrike's Kurtz told NBC News it "could be some time" before computers which were automatically rebooting to recover from the software glitch.

"Many of the customers are rebooting the system, and it's coming up and it'll be operational because we fixed it on our end. And some of the systems that aren't recovering, we're working with them. So it could be some time for some systems that just automatically won’t recover," he said.

The disaster has also raised concerns about the strength and safety of Australia's IT systems.

"It just shows we live in a highly connected software-enabled, so digitally connected world," Cyber Security Cooperative Research Centre CEO Rachael Falk told ABC Breakfast. "It's incredibly vulnerable when something goes down."

Falk said it should be a wake-up call for businesses and governments around the world—if this had been a cyber attack, the impacts would have been catastrophic.

"I think it shows that one system can bring down so many other organisations," she said.

Other cyber security experts called the outage "the worst thing" that could have happened given the unprecedented scale.

"This is more serious than a cyberattack because it shows our systems aren't even proofed against randomness," cybercrime professor Richard Buckland, from UNSW's School of Computer Science and Engineering, said.

Some experts believe there will be legal action against CrowdStrike and that the risk of cybersecurity has now Increased. 

Feature Image: Getty.