Schneier disagrees with active defense. From the post:
Because espionage unfolds over months or years in realtime, we can triangulate the origin of an exfiltration attack with some certainty. During the fog of a real cyber war attack, which is more likely to happen in milliseconds, the kind of forensic work that Mandiant did would not be possible. (In fact, we might just well be “Gandalfed” and pin the attack on the wrong enemy.)
“Gandalfed” cool word to indicate that you attack the wrong enemy, or attribute the attack to the wrong group. I agree with the post that we have not solved that attribution problem. I continue to argue that during the long millisecond where the attack is active, there is no need to attribute. There is simply a need to make the attack stop. Find out where the attack originates after you halt the attack with an appropriate use of force.