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Microsoft said early Saturday that it had fully restored its services after a global outage disrupted them for a day and a half, hampering communications and work at schools, government agencies and offices around the world.
The problems began on Thursday and cascaded around the world. The company, based in Redmond, Wash., gradually restored service through Friday until declaring an end to one of its most extensive outages of recent times in an update on Saturday around 1 a.m. Eastern time.
Here’s what to know.
What happened?
Outages started disrupting Microsoft tools and apps around noon Eastern time on Thursday and quickly spread to more than 70 countries and territories, affecting millions of users, according to Downdetector, an outage-tracking site.
Some of Microsoft’s most popular products, including the email manager Outlook, the workplace messaging and video calling app Teams and the artificial intelligence assistant Copilot, stopped working.
Was this a cyberattack?
Microsoft said in a statement on Friday that “for now, we can confirm that there is no indication this is the result of malicious or cyber activity.” It added that the problem was “a technical issue not related to cyber or A.I.” agents.
Was the F.A.A. ground stop linked to Microsoft?
The company said it had no indication that a Federal Aviation Administration ground stop issued late Friday afternoon, which has affected air travel nationwide, was related to the outage.
So why were Microsoft’s systems not working?
The company has yet to provide a clear answer, although it has promised to make public a full report identifying a “root cause.”
On Thursday, Microsoft said that a number of servers had unexpectedly shut down, straining the remaining infrastructure. On Friday, it said the problem had been introduced during a “network capacity upgrade.” It said it had addressed the underlying issue, allowing its tools and apps to begin functioning normally again.
“Given the scale of demand, we restored services gradually, validating stability at each stage,” it said. “While this took longer, it helped ensure a stable restoration.”
Luca Arnaboldi, an assistant professor of cybersecurity at the School of Computer Science at the University of Birmingham in England, said the outage was a reminder that when people use “the cloud,” they are actually relying on servers, which have finite resources.
“In this particular case, as servers became unavailable, capacity on the remaining servers increased, leaving fewer machines to handle the traffic,” he said in a statement. Even after some of the original servers came back online, he added, “the ones currently under strain now fail, creating a constant catch-up.”
Who was affected?
Parents struggled to contact their children’s schools, some government services faltered, and many office workers could not access email.
The outage affected parts of the U.S. government, including the House of Representatives, according to Samantha Carter, a spokeswoman for the office that oversees House operations.
Elsewhere in the world, the National Health Service in Britain said the outage had a “disruptive impact.” The National Pharmacy Association of Britain said the issues at the N.H.S. made it difficult for pharmacies to communicate with doctors and some patients, causing delays in filling prescriptions. The Metropolitan Police in London said its online contact forms stopped working.
