Emily Atkinson
Live page editor

It remains a little unclear exactly what caused the global IT outage that grounded thousands of flights, stalled banking and healthcare services, and badly hit other sectors today.

While there are signs of the chaos lifting, the question over quite how long the impacts persist remains - Crowdstrike says it could take "some time".

We're ending our live coverage now, but there's plenty on offer across the BBC to keep you updated in our absence:

• What caused the outage? And when will it be fixed? We answer the key questions here
• Blue screens, queues and airport delays worldwide. This minute-long video takes you through the main developments
• Has your flight been disrupted? Keep handy our guide to refunds, compensation and more
• Over on Newscast, Adam Fleming, Faisal Islam and Joe Tidy have been untangling the flawed Crowdstrike update
• Our technology editor Zoe Kleinman asks: was this the biggest outage ever? Check out her verdict

• Still after live updates? Follow our continuing live coverage here

This page was edited by Dulcie Lee, Aoife Walsh, Owen Amos, Barbara Tasch and Emily Atkinson. The writers were Ben Hatton, Seher Asaf, Rachel Flynn, Jamie Whitehead, Sofia Ferreira Santos, Anna Boyd, Shanaz Musafer and Hollie Cole.

Image source, EPA

Before we pack up for the night, here's digest of the key developments from across today:

• A massive tech failure has caused travel chaos around the world, with banking and healthcare services also badly hit
• Thousands of flights have been grounded because of the IT outage - a flaw which left many computers displaying blue error screens
• There were long queues, delays and flight cancellations at airports around the world, as passengers had to be manually checked in
• Cyber-security firm Crowdstrike has admitted that the problem was caused by an update to its antivirus software, which is designed to protect Microsoft Windows devices from malicious attacks

• Crowdstrike has said it has fixed the update, but admitted it could be "some time" before all systems are back up and running

Latest figures show more than 5,000 flights were cancelled worldwide following the global IT outage, which also caused major delays.

While queues continue to grow at some airports, for many passengers whose flights have been disrupted it's now a matter of finding a spot to bed down for the night.

Image source, EPA

Image source, EPA

Image source, Reuters

A massive tech failure has caused travel chaos around the world, with banking and healthcare services also badly hit.

We've wrapped up the key developments from across the day here:

Image source, Reuters

United Airlines says it has resumed some flights.

But the US airline says it expects schedule disruption throughout the day as it continues "to troubleshoot many systems and programs".

For those travelling today, it says it has issued a "travel waiver" to make it easier for passengers to change their plans.

Emma Vardy
Reporting from Austin, Texas

We’re in Austin, Texas outside the innocuous looking office block at the heart of the global IT meltdown.

In contrast to the chaos at airports, the main offices of Crowdstrike have very little visible activity.

No sign of any stressed employees frantically running to their desks, but we can only guess at the atmosphere inside.

Crowdstrike has a lot of questions to answer.

The news crews who were here earlier have hurried off to cover the human scenes of chaos and disruption elsewhere.

The CEO of Crowdstrike has turned down our request for an interview but has been on the airwaves on the American business news channel CNBC, promising that it will make sure that all customers recover from the outage.

Crowdstrike CEO George Kurtz says "nothing is more important" to him than the trust and confidence of the cybersecurity firm's customers and partners.

In a letter, external sent to its customers and partners, Kurtz apologises for the global IT outage and says Crowdstrike "understands the gravity and impact of the situation".

"We are working closely with impacted customers and partners to ensure that all systems are restored, so you can deliver the services your customers rely on," he says.

He urges people to only engage with official Crowdstrike representatives, adding that "bad actors" will try to "exploit" the situation.

"As we resolve this incident, you have my commitment to provide full transparency on how this occurred and steps we’re taking to prevent anything like this from happening again."

Image source, PA Media

The number of flights cancelled across the world after major IT disruption has risen to 5,078 – 4.6% of those scheduled – according to the latest update from aviation analytics firm Cirium.

In the UK, 167 departures have been cancelled – 5.4% of those scheduled – and 171 arrivals were cancelled, the firm says.

Several US airlines, including American, United and Delta, issued ground stops – an air traffic control measure that slows or grounds aircraft at a given airport – earlier as IT outages caused disruption across the globe.

This timelapse from flight-tracking website Flightradar24 below shows just how many flights were impacted.

Image source, Reuters

Payment systems have been among the IT systems impacted by today's disruption.

Morrisons said this morning it was experiencing “some issues” with payments in some stores, but around 40 minutes after it issued an update saying the problems had been fully resolved.

Posts on social media suggested some Waitrose stores were only taking cash payments for a time this morning.

The supermarket said it was briefly impacted earlier in the day, but it said this was limited to stores being unable to process contactless card payments, with chip and pin and cash payments still possible.

Asda, M&S, Tesco, Lidl, Sainsbury’s, Iceland and Lidl all said their stores operated as normal.

Co-op said it didn't experience any significant impact, and that cash and card payments were running as normal.

We can bring you some images now from New York City's Times Square, where some billboards went blank during today's IT outage.

Photos show black screens and "the blue screen of death" in place of the vibrant advertisements that typically light up the area.

Tom Harris, president of the Times Square Alliance, says a “handful” of the more than 100 billboards in the area remained offline earlier on Friday, AP reports.

He added that it's unclear whether all the blackouts were related to the outage.

Image source, Getty Images

Image source, Getty Images

Image source, Getty

We've seen over the last couple of hours that some airline services are beginning to return to normal following disruption.

Several say they expect delays and cancellations to persist through the weekend – and the latest images we've seen from airports around the globe suggest the long waits, at least for now, are here to stay:

Image source, EPA

Image source, Reuters

Image source, Reuters

Image source, EPA

What is Crowdstrike?published at 19:48 British Summer Time 19 July

19:48 BST 19 July

Liv McMahon
Technology reporter

Crowdstrike is a cybersecurity company founded in 2011 with the aim of safeguarding the world’s biggest companies and hardware from cyber threats and vulnerabilities.

It specialises in endpoint security protection and tries to prevent malicious software or files from hitting corporate networks from devices that connect to them, such as phones and laptops.

It also aims to protect the data of companies which have shifted from guarding it under their own roof, or on their own servers, to so-called cloud providers.

The Texas-based firm was co-founded by entrepreneurs George Kurtz, who remains chief executive, and Dmitri Alperovitch. It listed its shares publicly on the tech heavy Nasdaq stock exchange in 2019.

Since it first launched, the company has seemingly played a key role in helping firms investigate cyber-attacks.

In 2016 Crowdstrike was called in by the US Democratic National Committee, the strategy arm of the Democrat Party, to investigate a breach into its computer network.

Image source, Getty Images

Ambulance services have recorded higher than normal demand amid the IT outages today.

Some trusts pointed to the disruption suffered by other healthcare services during the IT disruption – GPs and pharmacies have been affected by outages, and some hospital appointments were also postponed.

The North East, South East Coast, South Central and London ambulance services have all recorded increased demand. The surge in London has been described as "huge".

Patients with the most serious or life-threatening conditions have been prioritised, with others being warned wait times could be impacted.

Image source, PA Media

We've just had an update from Gatwick, which says its IT systems are now operating as normal and it expects the "majority" of flights to operate as usual tomorrow.

“Some delays and cancellations will however continue this evening and over the weekend. We strongly advise passengers to check with their airline for the latest updates," a spokesperson says.

They add that there will be additional staff in the terminals this evening and some of the shops and eateries will remain open later than normal.

See our earlier post for the latest statements from some of the other large UK airports.

Big firms back online while disruption continues for smaller businessespublished at 19:10 British Summer Time 19 July

19:10 BST 19 July

Joe Tidy
Cyber correspondent

There’s an interesting and strange lesson amidst the chaos.

The biggest firms with the largest number of affected computers seem to be popping back up online the fastest.

This is what you’d expect, of course, but it possibly points to these larger richer companies having better resourcing of IT staff and better resilience measures in place.

The fix for this is largely a manual one and that means having IT staff at affected computers.

It’s the small and medium sized businesses that I think are struggling the most. They have fewer computers to fix but also fewer staff to go out and do the fixing.

For the big firms that make the headlines, this is largely proving to be short and sharp.

But, of course, we also don’t know what happens next with the backlogs of work, appointments, missed deadlines and general damage to organisations.

The most acute example of this is in airlines which are seemingly back online and running nearly normally, but with monstrous backlogs to work through.

The UK's National Cyber Security Centre (NCSC) is warning about an increase in phishing incidents in the wake of the global IT outage.

Phishing is when fraudsters send scam emails or text messages intended to trick users into revealing sensitive information and transfer money.

"An increase in phishing referencing this outage has already been observed, as opportunistic malicious actors seek to take advantage of the situation," the NCSC says in a statement.

It is urging organisations to review its guidelines to ensure protections against phishing are in place and calls on people to be alert to suspicious emails or messages.

A group of women on a hen do who were split up due to flight disruption caused by global IT problems are set to be reunited.

Some processes at East Midlands Airport, like check-in and boarding, had to be done manually after a defect in a software update by cyber-security firm Crowdstrike caused worldwide issues.

The group of 13 were set to fly from the airport to Dublin, but six of them who needed to check in luggage were delayed and missed their flight.

Undeterred, they were able to secure a later flight and are set to meet up with the bride-to-be and six others who departed earlier on Friday.

Flights have been delayed and cancelled across the US following the major global IT outage.

Here's a look at what's been happening on the ground at several airports:

Around 4,295 flights globally, or 3.9% of all scheduled services, have been cancelled so far today, according to aviation data from Cirium.

While the IT outage has caused some flights to be cancelled, this figure also includes those cancelled for other reasons.