CrowdStrike said that nearly all Microsoft Windows sensors are operational again after a faulty update by the cybersecurity company crippled computer systems across the world. 

More than 97% of Windows sensors were online as of Wednesday evening, CrowdStrike said in an update posted on its website. The systems are nearly fully restored after the company’s July 19 software update crashed millions of Windows-based devices and froze corporate networks.

Microsoft estimates the error took down 8.5 million Windows devices. The snafu will cost Fortune 500 companies more than $5 billion in losses, according to an estimate from Parametrix, an insurance services company. 

CrowdStrike CEO George Kurtz apologized for the outage in a LinkedIn post Thursday, assuring customers that the company was doing its best to fully restore computer systems. 

“I am deeply sorry for the disruption this outage has caused and personally apologize to everyone impacted. While I can’t promise perfection, I can promise a response that is focused, effective, and with a sense of urgency,” he wrote. 

CrowdStrike this week blamed the failure involving its Falcon security platform on a bug in a program designed to identify problems before customers are prompted to update their software. The resulted in “problematic content data” being sent to clients, CrowdStrike said on its website.  

The global outage highlights the fragility of interconnected  IT systems, according to experts. Consulting firm McKinsey & Company said the outage draws attention to “the trade-offs IT organizations must make between updating their environments to protect against cyberattacks versus managing changes that can introduce instability.”

Delta Air Lines, which was forced to cancel thousands of flights in the days after the outage, said Thursday that operations have returned to normal.