Authorites are investigating 9-1-1 phone line outages at emergency communications centers in four states.
Homeland Security officials have had concerns that the call centers could be the target of cyberattacks, NBC reported.
Millions in Nevada, Texas, South Dakota, and Nebraska were unable to use landlines to report emergencies during the issue Wednesday night.
During the disruption, residents were told to use their cell phones to contact 9-1-1. Those calls went through but dispatchers were not able to see the phone's number.
