LONDON (Reuters) - U.S. Fortune 500 companies, excluding Microsoft ( MSFT ), will face $5.4 billion in financial losses from the recent CrowdStrike ( CRWD ) outage, insurer Parametrix said on Wednesday.

CrowdStrike's ( CRWD ) faulty update to its security software crashed computers powered by Microsoft's ( MSFT ) 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.

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.