Websites for Heathrow, NatWest and Minecraft returned to service late on Wednesday after experiencing problems amid a global Microsoft outage.
Outage tracker Downdetector showed thousands of reports of issues with a number of websites around the world over several hours.
Microsoft said some users of Microsoft 365 saw delays with Outlook among other services, but by 21:00GMT, many websites that went down were once again accessible after the company restored a prior update.
The company’s Azure cloud computing platform, which underpins large parts of the internet, had reported a “degradation of some services” at 1600 GMT.
It said this was due to “DNS issues” – the same root cause of the huge Amazon Web Services (AWS) outage last week.
Amazon said AWS was operating normally.
Other sites that were impacted in the UK include supermarket Asda and mobile phone operator O2 – while in the US, people reported issues accessing the websites of coffee chain Starbucks and retailer Kroger.
The M&S website remained unavailable late on Wednesday, even after many others returned online.
Microsoft said business Microsoft 365 customers experienced problems.
Some web pages on Microsoft also directed users to an error notification that read “Uh oh! Something went wrong with the previous request.”
The tech giant resorted to posting updates to a thread on X after some users reported they could not access the service status page.
While NatWest’s website was temporarily impacted, the bank’s mobile banking, web chat, and telephone customer services remained available during the outage.
Meanwhile, business at the Scottish Parliament was suspended because of technical issues with the parliament’s online voting system.
The outage prompted a postponement of debate over land reform legislation that could allow Scotland to intervene in private sales and require large estates to be broken up.
A senior Scottish Parliament source told BBC News they believed the problems were related to the Microsoft outage.
Azure’s crucial role online
Exactly how much of the internet was impacted is unclear, but estimates typically put Microsoft Azure at around 20% of the global cloud market.
The firm said it believed the outage was a result of “an inadvertent configuration change”.
In other words, a behind-the-scenes system was changed, with unintended consequences.
The concentration of cloud services into Microsoft, Amazon and Google means an outage like this “can cripple hundreds, if not thousands of applications and systems,” said Dr Saqib Kakvi, from Royal Holloway University.
“Due to the cost of hosting web content, economic forces lead to consolidation of resources into a few very large players, but it is effectively putting all our eggs in one of three baskets.”
Recent outages have laid bare the fragility of the modern-day internet, according to engineering professor Gregory Falco of Cornell University.
“When we think of Azure or AWS, we think of a monolithic piece of technology infrastructure, but the reality is that it’s thousands, if not tens of thousands, of little pieces of a puzzle that are all interwoven together,” said Mr Falco.
He noted that some of those pieces are managed by the companies themselves while others are overseen by third parties such as CrowdStrike, which last year deployed a software update that affected more than eight million computers running on Microsoft systems.