The article appears flawed. It talks about e-terrorism and then accuses Nort Korea. However, covert attack by another state party is not terrorism, it is "diversionary activity", a form of warfare, like the WWII allied commando raids on the nazi heavy water factory and the night capture of a nazi mobile radar station on the occupied french coast.

Similarly if your own population does something nasty, it is not terrorism, it is "sabotage", like the intentional wrecking of industrial infrastructure by workers in nazi-occupied Europe during WWII.

USA is vulnerable to all of terrorism, diversion and sabotage, even in the e-sphere. The nation is easy to enter under false papers or outright illegally and there are a lot of non-yet-assimilated arab, muslim or chinese immigrant citizens, who could do e-sabotage. It is stupid to underestimate the dangers, because USA may be 3-8 years ahead in hardware, but the rest of the world has much better programmers. Asians and slavs are excellent at maths and they are hero programmers. They have already stolen all of the digital assets of USA and only their lag in hardware advances prevents them from  using that trove to further their own aims.