It seems like it was via an attachment in a phishing email that one of the employees clicked on...
"Milburn contacted Matthew Thomlinson, a Microsoft Corp. (MSFT) threat expert for help. Thomlinson found the malware had downloaded software that burrowed into the company’s Microsoft operating system, automatically uploading more tools the hackers could use to control the network remotely."
"Milburn contacted Matthew Thomlinson, a Microsoft Corp. (MSFT) threat expert for help. Thomlinson found the malware had downloaded software that burrowed into the company’s Microsoft operating system, automatically uploading more tools the hackers could use to control the network remotely."