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.

Hackers exploited a security flaw in common Microsoft Corp. software to breach governments, businesses and other organizations across the globe and steal sensitive information, according to officials and cybersecurity researchers.

Dozens of organizations appear to have been affected over the past few days by hackers targeting Microsoft server software. Microsoft said in a post on its website on Saturday that it was “aware of active attacks targeting on-premises SharePoint Server customers by exploiting vulnerabilities.