A mass IT outage has caused chaos around the world, with major banks, media outlets and airlines among the victims.
Many flights have been grounded, with queues and delays at airports, while shops and communications have also been hit.
The cause is unknown, but Microsoft says it is taking “mitigation action” to deal with “the lingering impact” of the outage.
Australia’s home affairs ministry and American Airlines have both said the outage appeared to be related to an issue at global cyber-security firm Crowdstrike.
Here is a summary of what we know so far.
The problem emerged in a piecemeal fashion, with first reports coming out of Australia.
Payment systems went down at Australian stores including Woolworths, while financial institutions such as the National Australia Bank were also affected.
Then the issues spread to the US. The state of Alaska warned that its emergency services were affected, while several of the country’s airlines – United, Delta and American Airlines – grounded their flights around the globe.
Australian carriers Virgin Australia and Jetstar also had to delay or cancel flights as departure screens went blank at Sydney airport.
Tokyo-Narita and Delhi airports said services had been affected. European airports reported that the outage was causing delays, with long queues reported at London’s Stansted and Gatwick and Amsterdam’s Schiphol.
Ryanair said it was experiencing “potential disruptions across the network”, which it said were due to a third-party outage.
Broadcasters were also caught up in the chaos, including Sky News in the UK, which is off air.
As the full extent of the disruption became clear, more firms and institutions started reporting problems.
The London Stock Exchange said it was working as normal, but there were issues with its news service, used by companies to report market-sensitive information in a timely way.
Israel says 15 hospitals have switched to manual processes but this has not affected medical treatment. Ambulances are being told to take new cases to other hospitals.
And Poland’s largest container terminal, the Baltic Hub in the northern city of Gdansk, has said the outage is “hampering terminal operations” and has asked companies not to send containers to the port.
In the UK, railway companies have reported delays and said they were experiencing “widespread IT issues”, while some doctors’ surgeries in England reported issues with booking appointments.
The problems have extended to upmarket UK bakery chain Gail’s, which has said it is currently unable to take in-store payments.
What precisely went wrong is still unclear.
However, a spokesperson for Australia’s Home Affairs Minister said the outage appeared to be related to an issue at global cyber-security firm Crowdstrike.
Australia’s National Cyber Security Coordinator described it as a “large-scale technical outage” and said there was no information to suggest it was an attack.
American Airlines, which is the world’s biggest by passenger numbers, told the BBC the IT problems were because of a “technical issue with Crowdstrike that is impacting multiple carriers.”
United Airlines told the BBC: “A third party software outage is impacting computer systems worldwide, including at United.”
There have been reports suggesting that Crowdstrike, which produces antivirus software, issued a software update that caused Windows devices to crash.
Crowdstrike shares plunged as much as 14% in early trade, and Microsoft also declined, as did travel and leisure stocks, as the disruptions threaten the holiday season.
The BBC has approached Crowdstrike for comment but has not yet heard back.
