The tech giants have evidence that Chinese hackers are exploiting the new bug, but warned "multiple actors" are also hacking into affected SharePoint systems.

A cyber-espionage campaign centered on vulnerable versions of Microsoft's server software now involves the deployment of ransomware, Microsoft said in a late Wednesday blog post.

Vulnerabilities in the software have allowed hackers to access file systems and execute code, the US Cybersecurity and Infrastructure Security Agency warned on Sunday.