An update to cybersecurity firm CrowdStrike’s (CRWD) security software caused an outage in Microsoft’s (MSFT) cloud services, disrupting airlines, banks, and other businesses worldwide Friday.

The outage sent shares of CrowdStrike tumbling 18% in premarket trading, while Microsoft stock fell more than 2% as the tech giant said the cybersecurity firm’s update of its Falcon software affected its Windows platforms.

“We have been made aware of an issue impacting Virtual Machines running Windows Client and Windows Server, running the CrowdStrike Falcon agent, which may encounter a bug check (BSOD) and get suck in a restarting state,” Microsoft said.

CrowdStrike Chief Executive Officer (CEO) George Kurtz confirmed the cybersecurity firm’s role in the outage, blaming an update “defect.”

“CrowdStrike is actively working with customers impacted by a defect found in a single content update for Windows hosts,” Kurtz said in a post on X. “Mac and Linux hosts are not impacted. This is not a security incident or cyberattack.

“The issue has been …

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