Hacking isn't that easy to trace. They could make a clean attempt on the pentagon if they wanted to and not need to worry. Theres a program out there I forget the name which allows you to bounce your hack around the world some 500 times before coming out at the target destination. The problem is that it's SLOW!!!!
Or they could take over other peoples computers and get them to run the hack. Government can trace whatever they like, but if the source is an innocent third party who didn't even know there computer was compromised....
The ones who get caught are usually the stupid ones. For instance, the people who hacked Valve and got HL2's source code, contacted Gabe Newell and was "making arrangements to work for Valve". The point was to get him to come to America to serve his crime here, but germany found out and arrested him there.











