They added a layer of aluminium mesh to the outer skin of the aircraft. Aluminium is one of the best conductors around, they even make power lines out of it. I think the purpose is that whenever lightning strikes it will travel through the mesh and away from the aircraft. Adding alu mesh to the 787 wing made the wing 2.5% heavier. Not sure how they test it thou. I remember watching a documentary about a super puma that crashed into the north sea because of a lightning strike to the tail rotor. The blades were carbon composite held in place by aluminium attachments. Whenever the lightning tried to travel between the carbon composite and the aluminium there was a massive build up of energy that caused some of the blades to break off. They traced the problem back to the fact that whenever the aircraft was certified a different tail rotor was used so the one on the aircraft that day wasn't lightning strike tested so it is an important test I just don't know how they do it but I'm sure it involves man made lightning.
more info here:
http://seattletimes.nwsource.com/htm..._boeing05.html