WASHINGTON (Reuters) -Delta Air Lines on Friday sued cybersecurity firm CrowdStrike in a Georgia state court after a global outage in July caused mass flight cancellations, disrupted travel plans of 1.3 million customers and cost the carrier more than $500 million.

Delta's lawsuit filed in Fulton County Superior Court called the faulty software update from CrowdStrike "catastrophic" and said the firm "forced untested and faulty updates to its customers, causing more than 8.5 million Microsoft Windows-based computers around the world to crash."

The July 19 incident led to worldwide flight cancellations and hit industries around the globe including banks, health care, media companies and hotel chains.

"Delta's claims are based on disproven misinformation, demonstrate a lack of understanding of how modern cybersecurity works, and reflect a desperate attempt to shift blame for its slow recovery away from its failure to modernize its antiquated IT infrastructure," CrowdStrike said late on Friday.

Delta, which said it has purchased CrowdStrike products since 2022, said the outage forced it to cancel 7,000 flights, impacting 1.3 million passengers over five days.

Delta said CrowdStrike is liable for over $500 million in out-of-pocket losses as well as for an unspecified amount of lost profits, expenditures, including attorneys' fees and "reputational harm and future revenue loss."

The incident prompted the U.S. Transportation Department to open an investigation.

"If CrowdStrike had tested the faulty update on even one computer before deployment, the computer would have crashed," Delta's lawsuit says. "Because the faulty update could not

be removed remotely, CrowdStrike crippled Delta's business and created immense delays for Delta customers."

Delta said that as part of its IT-planning and infrastructure, it has invested billions of dollars "in licensing and building some of the best technology solutions in the airline industry." CrowdStrike has questioned why Delta fared so much worse than other airlines and said it has minimal liability, something Delta rejected.

Last month, a senior executive at CrowdStrike apologized before Congress for the faulty software update.

Adam Meyers, a senior vice president at CrowdStrike, said the company released a content configuration update for its Falcon Sensor security software that resulted in system crashes worldwide. "We are deeply sorry this happened and we are determined to prevent this from happening again," Meyers said.