Computers at Australian retailer Woolworths froze with the blue screen of death. Cash register issues closed scores of McDonald’s branches in Japan. Tesla halted some production lines. 911 call centers in Alaska couldn’t operate. Airline passengers around the world faced chaos and uncertainty.

All because of a single IT update.

The update, delivered by cybersecurity company Crowdstrike to Microsoft Windows desktop and laptop computers, tipped the digital world into delays and closures. There were no remote or automatic fixes: Instead, each computer required a manual reboot, in some cases more than 15 times.

Crowdstrike saw its stock price finish down more than 11% on Friday, a clear sign of the damage done to its business.

For those impacted, Crowdstrike’s terms and conditions limit liability to “fees paid,” leaving customers eligible for a refund and nothing more. Those with cyber insurance will likely be checking the fine print of their policies to see what’s covered.

The chaos is a stark illustration of the vulnerability of global IT systems. An update gone wrong from a single company many hadn’t heard of before Friday morning brought retailers, banks, hospitals, production lines, and airlines to a halt. It’s a pressing reminder of how reliant we are on just a few companies.