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Microsoft has apologized after a nearly daylong global outage took down Outlook, Teams and the rest of its 365 lineup for millions of users, and it is pinning the problem on a network upgrade.

Getting into it: The outage began around 1pm ET Thursday and spread to more than 70 countries, according to outage tracker Downdetector, which logged as many as 130,000 reports for Outlook at its peak. Outlook, Teams, SharePoint and Microsoft’s AI assistant Copilot were all hit, and the services were mostly unusable as offices opened across Asia and Europe, with the problems dragging into Friday morning in the US. The outage disrupted the US House of Representatives, the UK’s National Health Service, London’s Metropolitan Police, Australian police and the Japanese government, along with airlines including Air India.

Microsoft first blamed heavy load on its systems, but later said a number of servers had unexpectedly gone offline and were failing automated health checks, putting strain on the rest of its network. On Friday, it said the problem was introduced during an earlier network capacity upgrade and had been fixed, with services gradually coming back online and email backlogs nearing normal levels. The company said it found no sign of a cyberattack and will release a full report on the root cause.

“We are deeply sorry for the disruption this incident has caused our customers and partners. We know the trust they place in our services and take that responsibility extremely seriously,” a Microsoft spokesperson said.

Roughly 430 million people use Microsoft 365, and the company’s stock dipped more than 2% in early trading Friday before leveling off. Rep. Josh Gottheimer, a former Microsoft employee, said he has asked for a briefing on what happened.

“Is there something that went on that’s nefarious here, or is this just something else? These outages occur in a lot of the companies, but the size of it and the length of it and the timing of it,” Gottheimer said.

The outage comes amid concerns that businesses and governments have become dangerously dependent on a handful of tech providers, a reliance that critics say, coupled with a significant uptick in cyberattacks globally, has left critical systems increasingly exposed. Thursday’s outage also drew comparisons to July 2024, when a faulty update from cybersecurity firm CrowdStrike crashed computers worldwide and grounded flights.