A top security researcher claims the massive SharePoint zero-day attack was fueled by a leak from a Microsoft partner program, giving hackers a critical head start.

Microsoft is issuing an emergency fix to close off a vulnerability in Microsoft’s 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.

Active SharePoint exploits since July 7 target governments and tech firms globally, risking key theft and persistent access.

More information has emerged on the ToolShell SharePoint zero-day attacks, including impact, victims, and threat actors.

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 and news reports.

Providing additional updates on the breach, Microsoft said in a blog post on Tuesday that two Chinese nation-state operators, Linen Typhoon and Violet Typhoon, exploited vulnerabilities in the internet-facing SharePoint servers.

A security patch released by Microsoft earlier this month failed to fully fix a critical flaw in the U.S. tech company's SharePoint server software that had been identified at a hacking competition in May,