Last week's destructive CrowdStrike update brought down some 8.5 million Windows devices, Microsoft estimates.

The update caused Windows systems to blue screen of death, and led to one of the largest mass outages in IT history.

Flights were grounded, bank systems went offline, and hospital appointments were canceled.

The 2017 WannaCry cyberattack is estimated to have impacted 'only' 300,000 computers in 150 countries.

"The issue has been identified and isolated, and a fix has been deployed. This was not a cyberattack," CrowdStrike said in a statement. However, the fix is manual and technical, meaning that many systems will take a while to be restored.

"The outage was caused by a defect found in a Falcon content update for Windows hosts," CrowdStrike CEO George Kurtz said.

"I want to sincerely apologize directly to all of you for the outage. All of CrowdStrike understands the gravity and impact of the situation."

He added that it would take “some time” for all systems to be fixed.