Recently the Associated Press obtained hundreds of pages of documents related to the 2006 "Cyber Storm" exercise. Most interesting is the part where the participants attacked the game computers and pissed the referees off:

However, the government's files hint at a tantalizing mystery: In the middle of the war game, someone quietly attacked the very computers used to conduct the exercise. Perplexed organizers traced the incident to overzealous players and sent everyone an urgent e-mail marked "IMPORTANT!" reminding them not to probe or attack the game computers.

"Any time you get a group of (information technology) experts together, there's always a desire, 'Let's show them what we can do,'" said George Foresman, a former senior Homeland Security official who oversaw Cyber Storm. "Whether its intent was embarrassment or a prank, we had to temper the enthusiasm of the players."

See also this. CyberStorm report here.