Faulty CrowdStrike update crashes millions of Windows PCs worldwide

On 19 July 2024, a faulty content update to CrowdStrike's Falcon security sensor caused millions of Windows computers to crash and display the "blue screen of death". The update was pushed to customers early in the day, and affected machines were often stuck in a boot loop.

The disruption spread quickly across sectors. Airlines grounded or delayed thousands of flights, banks and payment systems had problems, broadcasters went off air, and some hospitals postponed procedures. Many organisations had to fix machines one by one, often by hand, by booting into safe mode and deleting a faulty file.

CrowdStrike, a US cybersecurity firm, said the incident was not a cyberattack and later published an analysis blaming a bug in its testing and validation process. Microsoft estimated that about 8.5 million Windows devices were affected. The outage is widely regarded as one of the largest IT failures in history, and it showed how dependent critical services are on a few software providers. It is often cited when later cloud and software outages, including those at Microsoft, are discussed.