Vigilantes in the Cyberspace?

In 1998, a group called Electronic Disturbance Theater launched DDoS attack on pentagon computers, to which Pentagon responded by redirecting the requests to a Java applet programmed to issue contra offensive causing system crashes.
This raised questions whether should someone launch a counter offensive when an intrusion is detected? And is law enforcement capable of acting on such sort of crime. Since many companies and individuals experience with cyber crime and law enforcement are bad, since law enforcement is not able to do anything, many say that one should take matters in own hands.
This also raised a suspicion of what are the legal and ethical terms of vigilantism. This is very important since there are companies that offer such services, and this is turning into a big business. One such company is “The First Vigilante Corp.” whose employees told a story that once they traced the locations from where the attacks came, went to the location, broke in and stole the equipment used leaving a note “See how it feels?”.