"Hacking Back" is apparently commonplace and accepted in some developing countries so I have heard, but it is not in others. Japan has, as you would expect, taken the stance against hacking even if it is for righteous revenge.
A 15 year old kid in junior high school had criminal charges filed against him for illegally accessing the yahoo mail account of someone that previously stole his yahoo mail credentials.
That person is a 20 year old guy who he met via an online game. This guy apparently had the habit of trying to trick others into installing a program that would "make their character uber elite" which in fact it only just logged their key strokes and emailed the logs back to him.
This kid was apparently pretty smart (well, if you discount the part about him blindly running code from someone he met online...) and realized that this program just made his computer run slower. He realized it was malware so he uninstalled it, analyzed it and found out the email address of the guy. He then somehow inferred his password in which he illegally accessed his account, etc...
The guy was caught a couple months later using the same trick on other people and during the police investigation they found out that this kid had been illegally accessing his account which he had no idea about.
They tracked the kid down and now they both face criminal charges.