The number of companies and organizations compromised by a security vulnerability in Microsoft Corp.’s SharePoint servers is increasing rapidly, with the tally of victims soaring more than six-fold in a few days,

A sweeping cyber-espionage campaign organization centered on vulnerable versions of Microsoft's server software has now claimed about 400 victims, according to researchers at Netherlands-based Eye Security.

In ongoing hacks, Microsoft says it has identified two Chinese hacking groups taking advantage of a key software flaw.