CrowdStrike is denying Delta's claims it was to blame for thousands of flight disruptions

• CrowdStrike denies Delta's claims that the firm is responsible for thousands of flight disruptions.
• Delta's CEO Ed Bastian said the IT outage cost the airline $500 million.

CrowdStrike has rejected Delta Air Lines' claim that it is responsible for $500 million worth of damage caused by the IT outage on Friday July 19 resulting in thousands of flight disruptions.

In a letter sent to Delta on behalf of CrowdStrike signed by Michael Carlinsky, a co-managing partner at law firm Quinn Emanuel Urquhart & Sullivan, the Texas-based cybersecurity firm said it is "highly disappointed by Delta's suggestion that CrowdStrike acted inappropriately and strongly rejects any allegation that it was grossly negligent or committed misconduct."

Delta's CEO Ed Bastian told CNBC in an interview last week that the half-a-billion figure accounts for "not just the lost revenue, but the tens of millions of dollars per day in compensation and hotels."

The airline canceled thousands of flights over several days. It resorted to manually restarting up to 40,000 systems affected by the outage as disruptions by other airlines moderated to the tens and single digits.

When Bastian was asked if Delta would seek damages from CrowdStrike, he responded: "We have no choice."

"We're not looking to wipe them [CrowdStrike] out, but we're looking to make certain we get compensated — however they decide to — for what they cost us," Bastian added.

"Should Delta pursue this path, Delta will have to explain to the public, its shareholders, and ultimately a jury why CrowdStrike took responsibility for its actions — swiftly, transparently, and constructively — while Delta did not," the letter sent to the airline on Sunday said.

It said CrowdStrike's CEO George Kurtz contacted Bastian to offer on-site support, but he did not get a response.

"The letter speaks for itself. We have expressed our regret and apologies to all of our customers for this incident and the disruption that resulted," CrowdStrike said in a statement.

"Public posturing about potentially bringing a meritless lawsuit against CrowdStrike as a long-time partner is not constructive to any party. We hope that Delta will agree to work cooperatively to find a resolution."

The Delta CEO told CNBC that the company suggested it give free consulting advice but no other assistance.

CrowdStrike's letter said if Delta files a suit, it would need to explain "why Delta turned down free on-site help from CrowdStrike professionals who assisted many other customers to restore operations much more quickly than Delta."

The Department of Transportation opened an investigation into Delta to discover whether the airline followed the law and supported customers during the disruption.

It is unclear if Delta has filed a lawsuit yet. Delta did not respond immediately to a request for comment from Business Insider.