Of course it isn't. The only time something that's normally a crime isn't is when violence is self-defense. Absolutely nothing else in our system of law has a "he started it" defense. Leaving aside that no judge is going to accept that hacking is violence without legislative action that will never happen, the normal standards of self-defense could still never apply. Given that you can't know you've been hacked until after it's done, it would instead be retaliatory, which is naughty.
Some people above are debating whether stealing stolen stuff is a crime. The answer is: it's not stealing. That is still your stuff. If somebody grabs your shit right off your person, that's also assault, so you're free to tackle them to get it back. If they steal it off a table or something, you might have more of a problem; you're still not stealing, but depending on where you live and whether the prosecutor's got a bug up his ass, using force to retrieve your stuff might get you in trouble. Same for carjacking your stolen car, and if you don't somehow do it the same time it happens to you, I imagine using a gun like that would at least get you arrested anywhere, in court anywhere but Texas, and convicted anywhere north of the Mason-Dixon line.
The larger point here: hacking is not exactly the same as assault, theft, or trespass, and applying the same logic to it is something almost any good judge would refuse to do for fear of unintended consequences. For instance: since you don't know who's hacking you until you've checked them out, if you counter-hack them, you might wind up hacking the police. That's kind of a good thing from a civil rights standpoint, as it means they are on the same level as us, bound by the same natural consequences of their actions, but hacking the police would only be legal in a goddamn utopia. Furthermore, counter-hacking might theoretically lead you to the wrong person if you're not as skilled as your attacker. While this is not the reason trespass is illegal, one can easily imagine trying to steal your stuff back and getting the wrong house, and that's when you're looking for a physical location which you know is associated with a specific person. With counter-hacking, you're looking for a computer somewhere which may or may not belong to your attacker which may or may not have PID stored that is legitimately associated with said bastard.
So, the whole argument boils down to this: hacking is hacking. It is not other activities, and cannot be usefully treated as similar to other crimes. The closest other thing is wiretapping, and nobody asks if it's okay to do that in a retaliatory fashion. Because of historical computer culture stuff, it might be argued that hacking shouldn't always be illegal, but currently it is, so that is the very obvious answer to the original question of this article. They should've been asking "should counter-hacking be legal," and because of the potential for harm to uninvolved third parties, I am kind of surprised to find myself saying that it should definitely not be. Counter-hacking should never happen without a warrant, and evidence gathered by it needs to be scrutinized very closely to make sure the right guy is caught.
