To be honest, there are a few "suspects" that I have in mind. The first suspect that comes into my mind is North Korea, thats because of the recent tension between USA and NK. The second suspect would be ISIS, I'm pretty sure that they wouldn't attack us only in the physical world. I mean there are some hacking groups that are from ISIS so I wouldn't be surprised if this attack originated from them. Although it isn't likely, there's a possibility that it be a Russian hack, since it was first targeted in Ukraine and then to USA.