[Ghost of SVR4]

We put some pretty serious hardware in the upper atmosphere years back while testing our goodies. We could not take out anywhere near the size of the continental United States, we knocked out some lights and made a lot of stuff fuzzy on the radio, but we did not blast a 3500 miles wide diameter area.
I too used to freak at the idea of a single warhead floated up 300 miles would wipe us all out if it came up from the southern hemisphere. Fact is, it won’t. Do damage? Sure, knock out everything? nope. Beyond which, how does a non-state terrorist get a payload into orbit in the first place? They would have to work with a nation in order to do so.

[USFRIENDINVICTORIA]

The EMP Commission has an explanation about how it would work — way to complex for me to attempt to summarize here. Suffice it to say, it is convincing.

http://empcommission.org/

[aegiscg47]

EMP has become the Global Warming of military threats over the last few years. The effects are not as destructive as first thought and while it could knock out the power grid in the affected area, it could be fixed and back in order before we entered a "new stone age" or a "Mad Max" type of scenario. Second, it wouldn't affect military systems, and as noted above, whoever launched it would cease to exist in the counterattack.

I would be far more worried about some terrorist group driving trucks into power substations in major cities during the summer months. The resulting riots, looting, and mayhem would do far more damage than any EMP attack.