Harley,
Here is how Ballistic Missles are classified:
Short-range ballistic missile (SRBM), under 1,000 km : Medium-range ballistic missile (MRBM) 1,000 to 3,000 km : Intermediate-range ballistic missile (IRBM) 3,000 to 5,500 km : Intercontinental-range ballistic missile (ICBM) Over 5,500 km

And they can be launched in a number of ways, the most difficult to defend against in my oppinion would be lauch from a vessel at sea. Especially one not known to be a military asset of a forgein country, like an ocean cargo / container ship. They can also be launched off of land vehicles and it is believed that North Korea has done testing on an SLV (Space Launch Vehicle).