After a day of worldwide IT chaos caused by a global outage, the boss of the cyber security firm, Responsible, has said it could be some time before all systems are back up and running. Thousands of flights have been canceled. Banking and health care has been affected, including the NHS, and some TV channels have been taken off air. Millions of people have been affected. The problems were first reported in Australia before spreading across the world, including here, where there were delays and big queues at airports. The American cyber security firm, CrowdStrike, did finally come forward to admit a defect in a software update it had issued which crashed Windows devices. The company is deploying a fix, but not before widespread mayhem. Tonight, we'll be looking at exactly what happened and how it's affected patients, passengers, and businesses. Our first report is from our technology editor, Zoe Kleinman.

The world woke up this morning to global chaos.

Massive tech outages are impacting airlines, businesses, offices.

Thousands of flights grounded globally. Long queues frustrated passengers. There was nothing on the boards.

There was nothing.

There was no ground staff. In the UK, doctors' surgeries forced to let down patients.

We're going to have to cancel your appointment.

Businesses unable to serve customers. We'll try to receive a credit card payment. I just would not accept it. Credit card and debit card. Tv programs, abruptly taken off air. The cause? At CrowdStrike, we monitor trillions of cyber events. A single update from this US antivirus company. You may have never heard of the cyber security firm, CrowdStrike, before, but it has nearly 24,000 customers around the world, many of them huge organizations like airlines and banks.

We stop a lot of bad things from happening.

We're deeply sorry for the impact that we've caused to customers, to travelers, to anyone affected by this, including our companies.

We know what the issue is.

We're resolving and have resolved the issue now.

It's recovering systems that are out there. What went wrong? First of all, to be clear, This was not a hack or cyber attack. You don't need to change your passwords. A faulty update meant millions of Microsoft users saw this screen pop up. If you know it, it'll make you shiver. The blue screen of death. It pops up when there's a critical error affecting the operation of your PC, in this case, accompanied by an unending loop of trying and failing to restart and launch properly. It only affected machines running Microsoft, but there are a lot of them. And what's the fix? Well, it's not straightforward. Every single machine affected needs a manual reboot in safe mode, which is not as simple as turning it off and on again. Microsoft says some people have had to do it 15 times, so it could take a while. Spare a thought for IT departments.

There will be someone in CrowdStrike who will be in a lot of trouble right now for not getting this right. And there will be a lot of people working this weekend in businesses all over the world to try and fix this problem and to patch it up. But at the same time, this is the price we pay for being so reliant on digital infrastructure.

From travel chaos to grocery shop payment problems, there'll now be tough questions about the damage done by one faulty update. How did it slip through Microsoft's safety nets? The cybersecurity world still advises that it's a good idea to keep on top of software updates, although perhaps today is not the day to bang that particular drum. Zoe Kleiman, BBC News.

As we heard, the firm behind the outage, CrowdStrike, has held up its hands but admitted that it will take time for things to get back to normal. Our correspondent, Emma Vardy, is outside their headquarters in Austin, Texas. And as Zoe said, not many people People will have heard of this company, Emma, but it's accidentally created such chaos.

Well, CrowdStrike, based here in Austin, has gained a strong reputation in a relatively short space of time for providing very strong top IT security solution. So it's relied upon by lots of different companies. It operates in more than 100 countries around the world, and as well as IT security. It also gets called in to investigate hacks, and it does some of the detecting creative work about who the hackers are behind major cyber attacks. So the chief executive today has said he's deeply sorry for what happened. But as to why a routine software update caused so many problems, the question, the answer to that, isn't exactly clear. Some experts have speculated that perhaps it was a lack of testing which led to some weaknesses slipping through. But clearly, CrowdStrike is now going to face some credibility problems. Its stock price has fallen, and there are going to be questions over what repercussions software firms like this should face when floors cause major disruption.

Thank you very much. Emma Vardy reporting there. The outage has wreaked havoc on people's travel plans with thousands of flights canceled around the world. At UK airports, there have been huge queues and delays all on a day, which is supposed to be one of the year's busiest. Here's our transport correspondent, Katie Austin.

What a start to the summer holidays. At Gatwick Airport, passengers who should have been on planes were forced to wait out delays.

People are tired. They've been handing out water. The boards don't really say anything. It Hu Pim, BBC News.Let's have a final word with our technology editor, Zoe Kleinman. Zoe, all this just goes to show how dependent we are on IT and how vulnerable we are.I think it really highlights the fragility of our digital lives. We're encouraged now to increasingly be cashless. We're to go online, to get advice, to buy things, to make appointments. And this tech infrastructure that backs all of that up is essentially run by a handful of very large companies. And what we're seeing now is that if something goes wrong, the impact is really vast and really wide-ranging. And even once a fix comes into place, it still takes time, doesn't it, to get everything back together. There are some calls for people saying, actually, we shouldn't be so reliant on a few big companies for everything, while other people are saying, well, actually, if we have lots of smaller companies doing this stuff, then are we leaving ourselves more open to vulnerabilities, to weaknesses, to attacks? So it is a real dilemma, I think, but nobody has seen anything of this size. I've been covering outages now for a long time, and normally, they're over before they start. To see something like this have such a huge global impact, I think, is really going to make people sit up and think. It's certainly made people get cash out of the bank today, put pen to paper, and do some old-fashioned things, I suppose, that we haven't done for quite a while because we haven't had a choice.No, indeed. Thank you very much. Zoe Klein, our technology editor.

Hu Pim, BBC News.

Let's have a final word with our technology editor, Zoe Kleinman. Zoe, all this just goes to show how dependent we are on IT and how vulnerable we are.

I think it really highlights the fragility of our digital lives. We're encouraged now to increasingly be cashless. We're to go online, to get advice, to buy things, to make appointments. And this tech infrastructure that backs all of that up is essentially run by a handful of very large companies. And what we're seeing now is that if something goes wrong, the impact is really vast and really wide-ranging. And even once a fix comes into place, it still takes time, doesn't it, to get everything back together. There are some calls for people saying, actually, we shouldn't be so reliant on a few big companies for everything, while other people are saying, well, actually, if we have lots of smaller companies doing this stuff, then are we leaving ourselves more open to vulnerabilities, to weaknesses, to attacks? So it is a real dilemma, I think, but nobody has seen anything of this size. I've been covering outages now for a long time, and normally, they're over before they start. To see something like this have such a huge global impact, I think, is really going to make people sit up and think. It's certainly made people get cash out of the bank today, put pen to paper, and do some old-fashioned things, I suppose, that we haven't done for quite a while because we haven't had a choice.

No, indeed. Thank you very much. Zoe Klein, our technology editor.