Microsoft says it estimates that 8.5m computers around the world were disabled by the global IT outage.

It’s the first time a figure has been put on the incident and suggests it could be the worst cyber event in history.

The glitch came from a security company called CrowdStrike which sent out a corrupted software update to its huge number of customers.

Microsoft, which is helping customers recover said in a blog post: "We currently estimate that CrowdStrike’s update affected 8.5 million Windows devices."