A security patch Microsoft released this month failed to fully fix a critical flaw in the U.S. tech giant's SharePoint server software, opening the door to a sweeping global cyber espionage effort, a timeline reviewed by Reuters shows.

Microsoft has pointed the finger at three Chinese nation-state actors. Here's what we know, plus how to guard against future attacks.

A large-scale attack on Microsoft’s server software, SharePoint, has affected systems across the world. The following SharePoint versions are at issue: Microsoft SharePoint Server Subscription Edition,