The patches fix the security holes in more recent versions of SharePoint, but the 2016 version is still at risk.

Dubbed a “zero-day” because it leverages a previously undisclosed digital weakness, the hacks allow spies to penetrate vulnerable servers and potentially drop a backdoor to secure continuous access to victim organisations.

A major cyberespionage operation targeting Microsoft's SharePoint server software has compromised about 100 organizations worldwide. The operation exploits a zero-day vulnerability, allowing hackers to install backdoors on affected servers.