When asked if a Virtual Private Network, or VPN, was used to disguise the true location of the email user who made the threats, NPD responded:

"This was a concern that we had during our investigation. We were informed by Google as well as the MSP Michigan Cyber Command Center that a VPN was not used. We are relying on these agencies expertise in making that determination."

According to Microsoft, a VPN establishes a digital connection between your computer and a remote server owned by a particular VPN provider, creating a point-to-point tunnel that encrypts your personal data, masks your IP address, and lets you sidestep website blocks and firewalls on the internet.

VPN have become increasingly popular easy to use over the last few years. 

"The NPD, in a joint effort with Google LLC and the Michigan State Police, launched an investigation to trace the origins of the threatening email," the NPD said on Monday. "Through these efforts, we have pinpointed the source of the email to Nigeria."