That's a 30 year old scare. It was questionable in regard to the USSR and is an idiocy indicator when used in combination with terrorists or Iran etc etc

Jason Sigger battled the scaremongers for a while:

http://armchairgeneralist.typepad.co...p-crazies.html

http://armchairgeneralist.typepad.co...l-reports.html

http://armchairgeneralist.typepad.co...emp-crazy.html

http://armchairgeneralist.typepad.co...to-senate.html

http://armchairgeneralist.typepad.co...-of-crazy.html

http://armchairgeneralist.typepad.co...iscussion.html

http://armchairgeneralist.typepad.co...p-crazies.html

http://armchairgeneralist.typepad.co...concerned.html

http://armchairgeneralist.typepad.co...t-company.html

http://armchairgeneralist.typepad.co...p-threats.html

http://armchairgeneralist.typepad.co...p-effects.html

http://armchairgeneralist.typepad.co...to-europe.html

http://armchairgeneralist.typepad.co...es-attack.html

http://armchairgeneralist.typepad.co...out-there.html

and more, more, more...

Or this
http://dickdestiny.com/blog1/2010/06...ok-and-others/



I own an old book from about 1982, compiled by the FAS or some other scientists organisation (didn't see the book in a while). The chapter on EMP from 1982 mentioned that 4 500 kt (or was it 1 Mt?) warheads exploding in a patter over the U.S. at hundreds of kilometres altitude would have a good, but not at all all-frying effect on electronics.
It was a secondary concern when the USSR had thousands of nukes and operational SSBNs. It's a ridiculous concern now.