Microsoft fires back at Delta after massive outage, says airline declined 'repeated' offers for help

Microsoft fired back at Delta Air Lines on Tuesday accusing the carrier of not modernizing its technology before it canceled thousands of flights in the wake of last month's global massive IT outage.

Delta CEO Ed Bastian told CNBC last week that the carrier has "no choice" but to seek damages from Microsoft and CrowdStrike for the mass disruptions, which he said cost the company, an airline that prides itself on reliability, about $500 million.

Delta struggled more than rival airlines to recover from the outage, canceling more than 5,000 flights in the days following the July 19 incident, which was sparked by a botched software update from CrowdStrike and affected millions of computers running Microsoft Windows.

Mark Cheffo, a Dechert partner representing Microsoft, said in a letter Tuesday to Delta's attorney David Boies of Boies Schiller Flexner, said Microsoft is still trying to figure out why American Airlines, United Airlines and others were able to recover more quickly than Delta.

"Our preliminary review suggests that Delta, unlike its competitors, apparently has not modernized its IT infrastructure, either for the benefit of its customers or for its pilots and flight attendants,"Cheffo wrote.

Delta responded on Tuesday that it has "a long track record of investing in safe, reliable and elevated service for our customers and employees.

"Since 2016, Delta has invested billions of dollars in IT capital expenditures, in addition to the billions spent annually in IT operating costs," Delta said in response to the Tuesday letter from Microsoft," the airline said in a statement.

In a July 29 letter, Boies told Microsoft's chief legal officer, Hossein Nowbar: "We have reason to believe Microsoft has failed to comply with