Today's cyber-outage represents one of the most significant incidents in years - with some likening it to the 2017 WannaCry ransomeware attack which affected companies and state bodies around the world.
But while this outage was initially thought to be another malicious act, it quickly became clear that it was the result of an error by a single company.
That may be a relief to some - but the disruption it has led to still represents a major problem for companies and governments around the world.
Getting to grips with what happened - and fixing the problem - will not be an easy job, either.
What happened?
From the early hours of this morning onwards, users and companies with Windows devices started to see the dreaded 'Blue Screen of Death'.
That’s the error screen that appears on Microsoft’s operating system, which signals a critical failure.
The first reports came from Australia – where businesses were in the middle of their working day – before the issue began to pop up across Asia, Europe, Africa and the US and beyond.
While there were initial fears that the outage was the result of a cyber attack, it quickly became clear that this was down to a faulty software update pushed out by CrowdStrike.
It was intended as a regular upgrade to its anti-virus software – pushed out late at night (US time) to ensure minimal disruption. However a significant bug within its code meant the end result was the complete opposite.
CrowdStrike’s CEO George Kurtz described the issue as a "defect" in a "content update" for Windows.
What is CrowdStrike?
CrowdStrike is a US tech firm, founded just 13 years ago and headquartered in Austin, Texas.
While far from a household name, it has developed a serious reputation in business circles for its work in cybersecurity.
Part of that work has been in helping companies to recover from and investigate cyber-attacks – but it also offers protection of its own, including anti-virus software called Falcon.
In its most recent earnings results, CrowdStrike said it had almost 24,000 customers.
On its website, it references some of its big-name partners, including IBM, BT, Santander and Dell.
How did one piece of software have such a huge impact?
Even in the age of Apple and Android-powered smartphones, Microsoft’s Windows still represents the backbone of the world’s IT infrastructure.
That’s especially true when it comes to businesses.
Usually, Microsoft would not allow software made by a third party company to have the kind of access that would be required to cause problems for the entire Windows operating system.
This is done to ensure any mistakes or malicious activity can be contained.
But in order to provide adequate protection to the entire system, anti-virus software gets far greater system access than is normal.
Meanwhile CrowdStrike’s cybersecurity credentials – including its success in helping companies to clean up after cyber attacks – has made its Falcon software the go-to for big firms seeking to protect their systems.
That enhanced access – mixed with the popularity of CrowdStrike’s software – has ironically combined to create the kind of wide-scale vulnerability that anti-virus software is designed to protect against.
Who has been affected by the outage?
Businesses around the world and across countless industries.
Airlines including Ryanair, Wizz Air, United, Delta, American Airlines and Cathay Pacific have all reported issues; meanwhile airports like Gatwick, Brussels, Charles de Gaulle, Orly, Berlin and Edinburgh have also been seeing problems with their systems.
But even airlines and airports that were not directly affected by the outage have encountered problems, due to the knock-on effect of delays and outages.
Retailers including Morrisons and Ladbrokes in the UK, McDonalds in Japan and Woolworths in Australia all reported issues with payment systems, forcing some to accept cash only for a period of time.
Broadcasters including Sky News, CBBC, MTV and ESPN were forced off-air as a result of the outage.
Some health and emergency systems were impacted, including the NHS in the UK and some 911 services in the US.
Meanwhile many apps, including Transport for Ireland’s programmes, lost functions for a time, while the NCT also encountered problems.
How long will it take to fix?
It’s impossible to know for sure.
Microsoft says it is aware of the problem and expects a fix soon.
CrowdStrike said the issue had been "identified, isolated and a fix has been deployed".
However that will only serve to stop any further spread of this morning’s problem.
The real job will be fixing all of the devices that have already been hit by the Blue Screen of Death, which could take time.
When a device has a critical failure like this, simply restarting it is not possible. Remotely pushing out a fix to multiple devices is also not an option. (Although Microsoft suggests that some users might be able to overcome the problem through multiple reboots).
Instead, most users will likely have to reboot the device in ‘Safe Mode’, and then manually fix the error that prompted the blue screen in the first place.
But each of CrowdStrike’s 24,000 customers represents a company – each one with tens, hundreds, or even thousands of Windows devices.
This a big task for IT departments around the world which will now have to undertake the slow, manual process of correcting each machine.
