Microsoft has traced a major worldwide outage to a problem created during an earlier network-capacity upgrade, which emerged after a subsequent network change.
The company said it had fixed the underlying fault and was continuing to bring services back online for customers and regions affected by the disruption.
Microsoft also stressed that the incident was not linked to a cyberattack or AI agents.
“We are deeply sorry for the disruption this incident has caused our customers and partners.
“Given the scale of demand, we restored services gradually, validating stability at each stage. While this took longer, it helped ensure a stable restoration.
The outage hit Microsoft applications such as Outlook
“We will provide a full post-incident report once our review is complete,” the statement added.
Governments around the world were earlier forced to activate contingency plans as Microsoft worked to restore email, Teams and other services that went offline at about 6pm yesterday.
Downdetector, which tracks reports of online disruptions, recorded the first sharp rise in complaints about Microsoft Teams in Ireland and the UK at around 6.15pm yesterday. In the US, more than 130,000 users reported problems with Outlook at the height of the outage last night.
Millions of customers were unable to send or receive messages through Outlook. Teams was also unavailable to many users, while Microsoft’s Copilot AI assistant and other Microsoft 365 products were affected.
Several other AI chat platforms also experienced disruption, including OpenAI’s Chat GPT and Anthropic’s Claude.
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The failure affected businesses, police forces, health services and schools, making it one of the most serious IT disruptions seen in years.
Some police forces said they could not accept crime reports online and urged the public to use 101 or 999 for urgent reports.
The HSE said it had also been affected, like other customers, with emails failing to transmit.
Healthmail was among the services disrupted, creating difficulties for prescriptions. GPs and pharmacists were advised to issue paper prescriptions under the GMS scheme.
The HSE added that Microsoft video-conferencing services were experiencing intermittent problems, although no other services had been affected so far.
An Irish technology consultant said there were several possible reasons why Microsoft 365 services could have been caught up in the outage.
Microsoft said the outages did not appear to be the result of a cyber attack
Speaking on RTÉ’s Drivetime, Brian Honan said organisations across many sectors depend on Microsoft 365 for email, messaging, SharePoint, file sharing and communication with colleagues and clients.
He said the incident was not Microsoft’s first major outage, noting that a similar disruption occurred a year ago.
“The issue here is when you are using a single provider like that, you have concentrated risk. If anything happens to that provider, it will end up having a major impact throughout,” he said.
Switzerland, Denmark and the International Court of Justice have all moved away from Microsoft 365, he said, citing not only technical concerns but also questions around digital sovereignty and data protection.
Mr Honan said organisations that outsource their systems to a third party still remain responsible for maintaining their services.
Businesses, he added, need to assess how an outage would affect their operations before relying on a provider.
“You don’t have any direct control over this, so you are relying on the third party to bring it back up and running,” he said.
