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.

Security researchers say Microsoft customers should take immediate action to defend against the ongoing cyberattacks, and must assume they have already been compromised.

The newly discovered flaw in Microsoft's SharePoint software has allowed hackers to target dozens of companies and organizations. Only a partial fix has been issued.

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

The hackers behind the initial wave of attacks exploiting a zero-day in Microsoft SharePoint servers have so far primarily targeted government organizations, according to researchers as well as news reports.

Microsoft Corp. advirtió que piratas informáticos están atacando activamente a los clientes de su software de gestión de documentos SharePoint, y los investigadores de seguridad han señalado el riesgo de que se produzcan violaciones de seguridad a gran escala en todo el mundo.

Hackers have been exploiting a vulnerability to attack SharePoint and connected Microsoft services in what will be a big problem for corporate Mac users this week.