Microsoft issued an emergency fix to close off a vulnerability in its SharePoint software that hackers have exploited to carry out widespread attacks on businesses and at least some federal agencies.

Microsoft's SharePoint software is under active attacks, posing a threat to businesses and governments worldwide due to a vulnerability allowing unauthenticated system access.

Researchers say Chinese actors, along with other criminal hackers, exploited a security flaw in SharePoint software widely used by governments and businesses.

Microsoft said the company has been "coordinating closely with CISA, DOD Cyber Defense Command, and key cybersecurity partners around the world throughout our response."

A global attack on Microsoft server software used by thousands of government agencies and businesses to share documents within organisations is likely the work of a single actor, a cybersecurity researcher said on Monday.

Microsoft has alerted organizations about active attacks exploiting a vulnerability in SharePoint servers, impacting over 10,000 on-premise installations, including those at businesses and government agencies.

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Britain's National Cyber Security Centre (NCSC) said on Monday it had detected a "limited number" of UK-based victims in an ongoing hacking campaign that has affected servers using Microsoft's SharePoint system.