U.S. Fortune 500 companies, excluding Microsoft, will face $5.4 billion in financial losses from the recent CrowdStrike outage, insurer Parametrix said Wednesday.

CrowdStrike's faulty update to its security software crashed computers powered by Microsoft's Windows operating system, disrupting internet services across the globe and affecting a broad swathe of industries including airlines, banking and healthcare.

Insured losses from the outage will likely total $540 million to $1.08 billion for the Fortune 500 companies, Parametrix said in a statement.

The outage was likely to be "the biggest accumulation event we ever saw in cyber insurance," Parametrix CEO Jonatan Hatzor told Reuters.

"This event traveled very fast and was very global."

Hatzor estimated that financial losses globally from the outage could total around $15 billion, as companies struggle to get their computers back up to speed. Global insured losses could total around $1.5-3 billion, Hatzor added.

Major cyber insurer Beazley said this week it had no plans to change its guidance on its combined ratio - a key measure of underwriting profitability - after the mass IT outage.

The global insurance and reinsurance industry is likely to avoid any major financial impact from the outage, ratings agency Fitch said on Monday.