It remains unclear who is behind the ongoing operation, which targeted around 100 organisations over the weekend. But Alphabet's Google, which has visibility into wide swathes of internet traffic, said it tied at least some of the hacks to a "China-nexus threat actor".

The Chinese Embassy in Washington did not respond to a Reuters request for comment. Chinese government-linked operatives are regularly implicated in cyberattacks, but Beijing routinely denies carrying out hacking operations.

Contacted on Tuesday, Microsoft was not immediately able to provide comment on the patch and its effectiveness.

The vulnerability that facilitated the attack was first identified in May at a hacking competition, opens new tab in Berlin organised by cybersecurity firm Trend Micro, which offered cash bounties for the discovery of computer bugs in popular software.

It offered a $100 000 prize for "zero day" exploits, so called because they leverage previously undisclosed digital weaknesses,  that could be used against SharePoint, Microsoft's flagship document management and collaboration platform.

A researcher working for the cybersecurity arm of Viettel, a telecommunications firm operated by Vietnam's military, identified a SharePoint bug at the event, dubbed it 'ToolShell' and demonstrated a method of exploiting it.

The researcher was awarded $100 000 for the discovery, according to a post on X by Trend Micro's "Zero Day Initiative". A Spokesperson for Trend Micro did not immediately respond to Reuters' requests for comment regarding the competition on Tuesday.

Microsoft subsequently said in a July 8 security update that it had identified the bug, listed it as a critical vulnerability, and released patches to fix it.

Around 10 days later, however, cybersecurity firms started to notice an influx of malicious online activity targeting the same software the bug sought to exploit: SharePoint servers.

--Reuters--