Banks, airlines, railways and media outlets have been hit by a global Microsoft outage.

Windows PCs inexplicably started showing a “blue screen of death” error that left them unusable.

According to cyber security companies, issues have been found across the world.

The problem appears to be related to a broken cyber security update that left computers unable to start up.

Sky News is offline, airports are unable to check in flights, trains were disrupted and banks warned that customers might not be able to make payments.

Companies affected by the outage include:

• Delta Airlines
• Visa
• Mastercard
• Lloyds Bank
• Santander
• Amazon
• RyanAir
• Sky News
• Ladbrokes
• BT
• Microsoft Teams

In the United States, Delta, United and American Airlines were all grounded.

UK train operator Govia Thameslink Railway, which runs the Southern, Thameslink, Gatwick Express and Great Northern services around London said it was experiencing “widespread IT issues”.

It means trains might be cancelled at short notice.

On Sky News, viewers were shown an error message that indicated the transmission had gone down.

It read: “We apologise for the interruption to this broadcast.

“We hope to restore the transmission of Sky News shortly.”

The trouble appears to be due to an issue at cyber security company Crowdstrike.

In an update, it said it had identified the issue and rolled the update back. However, the affected computers do not appear to have been fixed.

On the company’s Reddit thread, representatives advised that the problem could be fixed by deleting the update and then restarting the computer.

That requires administrators to have access to the computer, however, which may not be immediately possible for those that are being used remotely.

Ilkka Turunen, of the software supply chain management firm Sonatype, said:

“The widespread outages across the world affecting Microsoft Windows are due to a botched update to a piece of software called Crowdstrike, a well-regarded malware and endpoint protection tool often used by enterprises and many companies across the world.

“In terms of technical details, the update causes a BSOD loop on any Windows machine essentially making it boot and crash on an infinite loop.

“Making it worse is the fact that there are a significant number of Windows machines that the update was auto-installed on overnight.

“There are workarounds that customers of theirs will apply, but it seems to be very manual.”

“It’s definitely a supply chain style incident – what it shows is that one popular vendor botching an update can have a huge impact on its customers and how far a single well-orchestrated update can spread in a single night.

“It’s not yet clear if the contents were due to malicious reasons, but it shows how quickly targeted attacks on popular vendors could spread.”