Chinese "threat actors" have hacked Microsoft's SharePoint document software servers and targeted the data of the businesses using it, the firm has said.

Axar.az reports citing foreign media.

China state-backed Linen Typhoon and Violet Typhoon, as well as China-based Storm-2603, were said to have "exploited vulnerabilities" in on-premises SharePoint servers, the kind used by firms, but not in its cloud-based service.

The US tech giant has released security updates in response and has advised all on-premises SharePoint server customers to install them.

"Investigations into other actors also using these exploits are still ongoing," Microsoft said in a statement.

The firm said it had "high confidence" that the hackers would continue to target systems that have not installed its security updates.

It added that it would update its website blog with more information as its investigation continues.

Microsoft said it had observed attacks in which hackers had sent a request to a SharePoint server, "enabling the theft of the key material by threat actors".

Charles Carmakal, chief technology officer at Mandiant Consulting firm, a division of Google Cloud, told the BBC it was "aware of several victims in several different sectors across several global geographies".

Carmakal said it appeared that governments and businesses that use SharePoint on their sites were the primary target.

Several adversaries who stole material encoded by cryptography were then able to regain ongoing access to the victims' SharePoint data, he said.