WASHINGTON, Oct 28 (Reuters) - Cybersecurity firm

CrowdStrike ( CRWD ) said on Monday it sued Delta Air Lines ( DAL )

in U.S. District Court in Georgia after a faulty

software update prompted a global outage in July.

The July 19 incident led to worldwide flight cancellations

and hit industries including banks, healthcare, media companies

and hotel chains.

CrowdStrike ( CRWD ) said it sued to make clear that CrowdStrike ( CRWD ) did

not cause the harm that Delta claims, and that Delta repeatedly

refused assistance from both CrowdStrike ( CRWD ) and Microsoft ( MSFT ).

Delta did not immediately comment on CrowdStrike's ( CRWD ) suit.

CrowdStrike ( CRWD ) is seeking a declaratory judgment plus legal

fees.

Delta's lawsuit filed on Friday in Fulton County Superior

Court called the faulty software update from CrowdStrike ( CRWD )

"catastrophic" and said the company "forced untested and faulty

updates to its customers, causing more than 8.5 million

Microsoft Windows-based computers around the world to crash."

Delta said the faulty update caused 7,000 flight

cancellations, disrupted travel plans of 1.3 million customers

and cost the carrier more than $500 million.

CrowdStrike's ( CRWD ) lawsuit, also filed on Friday, said Delta's

own response and technology caused delays in the carrier's

ability to resume normal operations.

CrowdStrike's ( CRWD ) lawsuit reiterated its contention that it has

minimal liability, something Delta rejected.

Delta said CrowdStrike ( CRWD ) is liable for over $500 million in

out-of-pocket losses as well as for unspecified lost profits,

expenditures - including legal fees - reputational harm and

future revenue loss.

The incident prompted the U.S. Transportation Department to

open an investigation.

"If CrowdStrike ( CRWD ) had tested the faulty update on even one

computer before deployment, the computer would have crashed,"

Delta's lawsuit says.

Delta said it has invested billions of dollars in

information technology licensing and infrastructure.

Last month, a senior CrowdStrike ( CRWD ) executive apologized before

Congress for the faulty software update.