In a Forbes.com article, Richard Clarke, former anti-terrorism czar, says that US is at the bottom in defense when it comes to nations that have cyberwar capabilities.
In his new book, Cyberwar: The Next National Security Threat And What To Do About It, Clarke states that cyber defense depends on how porous a nations electronic borders are. And this is where the US is very vulnerable. Nations like China and N. Korea can disconnect from the grid much easier than the US.
On the positive side, Clarke lists the US as number one in cyber attack capabilities, followed by Russia, China, and Iran. North Korea comes in near the bottom of the list. This is probably a good thing as recently North Korea threatened the US with possible nuclear strike over its joint military exercise with South Korea.