There's another story suggesting that the US could hack into North Korea's missile systems and invoke malware if any missiles actually approached the IS. Missiles toward Japan or South Korea (more likely) would allow much less time for detection. The story appeared on Business Insider.
Update: April 15
North Korea displayed ICBM canisters in a military parade today, suggesting it could have (or soon have) missiles capable of reaching some parts of the U,S., or that it might have submarine launch capabilities, CNN story. Yet today we did not see a nuclear weapons test.
A North Korean intermediate range missile test from NE North Korea failed and exploded seconds after launch, BBC story, American NSA hackers could have been involved. North Korea's plan seems to be to survive a pre-emptive strike, if it can build several nuclear ICBM's capable of reaching the US
Here is ABC's account on "what to know now".